diff --git a/src/part1/constants.py b/src/part1/constants.py
index 9abfbba2..afc19ecf 100644
--- a/src/part1/constants.py
+++ b/src/part1/constants.py
@@ -1,38 +1,15 @@
-"""Bit layout and default epoch for the Twitter Snowflake ID generator.
-
-A Snowflake identifier is a 63-bit positive integer packed as follows, from
-the most significant bit downwards:
-
-    1 bit   unused sign bit, always zero
-    41 bits milliseconds elapsed since a custom epoch
-    10 bits node identifier
-    12 bits per-millisecond sequence counter
-
-The shift and mask constants should be derived from the bit widths so that
-changing a width keeps everything else consistent.
-"""
-
 from typing import Final
 
 
-# TODO: замените заглушки (0) на корректные значения, см. TASK.md.
-# Все константы, зависящие от ёмкостей *_BITS, должны вычисляться из них.
-
-# Twitter's original Snowflake epoch: 2010-11-04 01:42:54.657 UTC.
-EPOCH_MS_DEFAULT: Final[int] = 0
+EPOCH_MS_DEFAULT: Final[int] = 1288834974657
 
-# Node identifier used when the caller does not supply one.
-NODE_ID_DEFAULT: Final[int] = 0
+NODE_ID_DEFAULT: Final[int] = 1
 
-# Width of each field, in bits.
-TIMESTAMP_BITS: Final[int] = 0
-NODE_ID_BITS: Final[int] = 0
-SEQUENCE_ID_BITS: Final[int] = 0
+TIMESTAMP_BITS: Final[int] = 41
+NODE_ID_BITS: Final[int] = 10
+SEQUENCE_ID_BITS: Final[int] = 12
 
-# Largest value each field can hold.
-TIMESTAMP_MS_MAX: Final[int] = 0
-NODE_ID_MAX: Final[int] = 0
-SEQUENCE_ID_MAX: Final[int] = 0
 
-# Здесь можно добавить собственные вспомогательные константы
-# (например, сдвиги полей при сборке идентификатора).
+TIMESTAMP_MS_MAX: Final[int] = 2**TIMESTAMP_BITS - 1
+NODE_ID_MAX: Final[int] = 2**NODE_ID_BITS - 1
+SEQUENCE_ID_MAX: Final[int] = 2**SEQUENCE_ID_BITS - 1
diff --git a/src/part1/snowflake.py b/src/part1/snowflake.py
index d3abf050..13997f48 100644
--- a/src/part1/snowflake.py
+++ b/src/part1/snowflake.py
@@ -1,85 +1,38 @@
-"""Twitter Snowflake identifier generator.
+import time
 
-Snowflake produces roughly time-ordered 64-bit integer identifiers without
-coordination between nodes. Each identifier packs the milliseconds elapsed
-since a custom epoch, a node identifier and a per-millisecond sequence counter
-into a single 63-bit positive integer (see ``constants`` for the layout).
-
-The public entry point is :func:`generate_snowflake_id`. It is stateless: the
-caller passes the sequence counter on every call and is responsible for
-advancing it within a millisecond and resetting it when the clock ticks over.
-
-Each packed field can be read back on its own with :func:`decode_timestamp_ms`,
-:func:`decode_node_id` and :func:`decode_sequence_id`.
-"""
-
-import time  # noqa: F401
-
-from .constants import (  # noqa: F401
+from .constants import (
     EPOCH_MS_DEFAULT,
+    NODE_ID_BITS,
     NODE_ID_DEFAULT,
     NODE_ID_MAX,
+    SEQUENCE_ID_BITS,
     SEQUENCE_ID_MAX,
     TIMESTAMP_MS_MAX,
 )
 
 
 def read_current_millis(epoch_ms: int) -> int:
-    """Read the number of milliseconds elapsed since the custom epoch.
+    current_time = int(time.time() * 1000)
 
-    Args:
-        epoch_ms: The custom epoch expressed as Unix milliseconds.
-
-    Returns:
-        The count of whole milliseconds between ``epoch_ms`` and now. May be
-        negative if ``epoch_ms`` lies in the future.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    return current_time - epoch_ms
 
 
 def decode_timestamp_ms(snowflake_id: int, epoch_ms: int = EPOCH_MS_DEFAULT) -> int:
-    """Read the timestamp field out of a Snowflake identifier.
-
-    Args:
-        snowflake_id: An identifier produced against the same epoch.
-        epoch_ms: The epoch the identifier was generated against. Defaults to
-            the original Twitter epoch (2010-11-04 01:42:54.657 UTC).
+    default_time = snowflake_id >> (NODE_ID_DEFAULT + SEQUENCE_ID_BITS)
 
-    Returns:
-        The absolute Unix time in milliseconds at which the identifier was
-        generated.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    return default_time + epoch_ms
 
 
 def decode_node_id(snowflake_id: int) -> int:
-    """Read the node identifier field out of a Snowflake identifier.
+    node_id = (snowflake_id >> 12) & NODE_ID_BITS
 
-    Args:
-        snowflake_id: An identifier produced by :func:`generate_snowflake_id`.
-
-    Returns:
-        The node identifier packed into ``snowflake_id``, in the range
-        ``[0, NODE_ID_MAX]``.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    return node_id
 
 
 def decode_sequence_id(snowflake_id: int) -> int:
-    """Read the sequence counter field out of a Snowflake identifier.
-
-    Args:
-        snowflake_id: An identifier produced by :func:`generate_snowflake_id`.
+    sequence_id = snowflake_id & SEQUENCE_ID_BITS
 
-    Returns:
-        The per-millisecond sequence counter packed into ``snowflake_id``, in
-        the range ``[0, SEQUENCE_ID_MAX]``.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    return sequence_id
 
 
 def generate_snowflake_id(
@@ -87,28 +40,18 @@ def generate_snowflake_id(
     node_id: int = NODE_ID_DEFAULT,
     epoch_ms: int = EPOCH_MS_DEFAULT,
 ) -> int | None:
-    """Build and return a Snowflake identifier for the current millisecond.
-
-    The function is stateless: the caller passes the per-millisecond sequence
-    counter explicitly. It is the caller's responsibility to increment
-    ``sequence_id`` for identifiers minted within the same millisecond and to
-    reset it once the clock advances.
-
-    Args:
-        sequence_id: The per-millisecond sequence counter, in the range
-            ``[0, SEQUENCE_ID_MAX]``.
-        node_id: The identifier of this node, in the range ``[0, NODE_ID_MAX]``.
-            Optional; defaults to ``NODE_ID_DEFAULT``.
-        epoch_ms: The start of the epoch as Unix milliseconds. Optional;
-            defaults to the original Twitter epoch (2010-11-04 01:42:54.657
-            UTC).
-
-    Returns:
-        The Snowflake identifier as a positive 63-bit integer, or ``None`` if
-        ``node_id`` is outside ``[0, NODE_ID_MAX]``, ``sequence_id`` is outside
-        ``[0, SEQUENCE_ID_MAX]``, or the elapsed time no longer fits in the
-        timestamp field (roughly 69 years after ``epoch_ms``). In each of those
-        cases an explanatory message is printed to stdout first.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    if node_id < 0 or node_id > NODE_ID_MAX:
+        print("node_id must be in range[0; 1023]")
+        return None
+    elif sequence_id < 0 or sequence_id > SEQUENCE_ID_MAX:
+        print("sequence_id must be in [0; 4095]")
+        return None
+    elif decode_timestamp_ms(epoch_ms) > TIMESTAMP_MS_MAX:
+        print("overflows")
+        return None
+
+    return (
+        read_current_millis(epoch_ms) << (NODE_ID_BITS + SEQUENCE_ID_BITS)
+        | node_id << SEQUENCE_ID_BITS
+        | sequence_id
+    )
diff --git a/src/part2/cart.py b/src/part2/cart.py
index 063f9aea..a53f3570 100644
--- a/src/part2/cart.py
+++ b/src/part2/cart.py
@@ -1,20 +1,10 @@
-"""Shopping-cart operations layered on top of the product store.
-
-The cart is a plain list of tuples, one :data:`CartLine` --
-``(product_id, quantity)`` -- per distinct product. Moving units between the
-store and the cart keeps the two sides in balance: :func:`add_to_cart` takes
-units out of stock, :func:`remove_from_cart` puts them back.
-
-Like the CRUD layer, the failure path never raises -- the operation prints
-an explanatory message to stdout and returns ``None``.
-"""
-
 from typing import Final
 
-from .crud import read_product, update_product  # noqa: F401
-from .storage import (  # noqa: F401
+from .crud import read_product, update_product
+from .storage import (
     NAME_INDEX,
     PRICE_INDEX,
+    PRODUCT_ID_INDEX,
     QUANTITY_INDEX,
     Product,
 )
@@ -24,7 +14,7 @@
 
 # TODO: задайте позиции полей внутри кортежа CartLine
 LINE_PRODUCT_ID_INDEX: Final = 0
-LINE_QUANTITY_INDEX: Final = 0
+LINE_QUANTITY_INDEX: Final = 1
 
 
 def add_to_cart(
@@ -33,28 +23,50 @@ def add_to_cart(
     product_id: int,
     quantity: int,
 ) -> CartLine | None:
-    """Move ``quantity`` units of ``product_id`` from the store into ``cart``.
-
-    The product is looked up in ``storage``. If it is missing, a message is
-    printed (by :func:`~src.part2.crud.read_product`) and nothing
-    changes. If the store holds fewer units than requested, an explanatory
-    message is printed and nothing changes. Otherwise the store record is
-    decremented by ``quantity`` and the cart line for ``product_id`` gains
-    ``quantity`` units -- a new line is created when the cart had none.
-
-    Args:
-        storage: The product store to draw stock from; modified in place on
-            success.
-        cart: The cart to add the units to; modified in place on success.
-        product_id: The identifier of the product to add.
-        quantity: Number of units to move into the cart.
-
-    Returns:
-        The cart line for ``product_id`` after the addition, or ``None``
-        when the product is unknown or the store cannot cover the request.
-    """
-    # TODO: реализуйте функцию
-    return (0, 0)
+    product = read_product(storage, product_id)
+    if product is None:
+        return None
+
+    for i in range(len(storage)):
+        product = storage[i]
+        if product_id == product[PRODUCT_ID_INDEX]:
+            quantity_storage = product[QUANTITY_INDEX]
+            if quantity > quantity_storage:
+                print(
+                    f"not enough stock for product <{product_id}>: {quantity_storage} available, {quantity} requested"
+                )
+                return None
+
+            name, price = product[NAME_INDEX], product[PRICE_INDEX]
+            new_product = (product_id, name, price, quantity_storage - quantity)
+            storage[i] = new_product
+
+            for j in range(len(cart)):
+                cur_cart = cart[j]
+                if cur_cart[LINE_PRODUCT_ID_INDEX] == product_id:
+                    new_cart = (
+                        cur_cart[LINE_PRODUCT_ID_INDEX],
+                        cur_cart[LINE_QUANTITY_INDEX] + quantity,
+                    )
+                    cart[j] = new_cart
+                    return new_cart
+
+            new_cart = (product_id, quantity)
+            cart.append(new_cart)
+            return new_cart
+
+    return None
+
+
+def find_cart_line(
+    cart: list[CartLine],
+    product_id: int,
+) -> CartLine | None:
+    for product in cart:
+        if product_id == product[LINE_PRODUCT_ID_INDEX]:
+            return product
+
+    return None
 
 
 def remove_from_cart(
@@ -63,27 +75,38 @@ def remove_from_cart(
     product_id: int,
     quantity: int,
 ) -> CartLine | None:
-    """Move ``quantity`` units of ``product_id`` from ``cart`` back to the store.
-
-    The cart line for ``product_id`` is looked up. If there is none, a
-    message is printed and nothing changes. If the line holds fewer units
-    than requested, an explanatory message is printed and nothing changes.
-    Otherwise the cart line loses ``quantity`` units -- the line is dropped
-    when it reaches zero -- and the store record gains ``quantity`` units
-    back.
-
-    Args:
-        storage: The product store to return stock to; modified in place on
-            success.
-        cart: The cart to take the units from; modified in place on
-            success.
-        product_id: The identifier of the product to remove.
-        quantity: Number of units to move back into the store.
-
-    Returns:
-        The cart line for ``product_id`` after the removal (a quantity of
-        zero means the line was dropped), or ``None`` when the cart has no
-        line for the product or holds too few units.
-    """
-    # TODO: реализуйте функцию
-    return (0, 0)
+    cart_line = find_cart_line(cart, product_id)
+
+    if cart_line is None:
+        print(f"product <{product_id}> is not in the cart")
+        return None
+
+    for i in range(len(cart)):
+        id, quantity_cart = cart[i]
+        if id == product_id:
+            if quantity > quantity_cart:
+                print(
+                    f"cart holds only {quantity_cart} unit(s) of product <{product_id}>, cannot remove {quantity}"
+                )
+                return None
+
+            product = read_product(storage, product_id)
+            if product is None:
+                return None
+
+            new_product = (
+                product[NAME_INDEX],
+                product[PRICE_INDEX],
+                product[QUANTITY_INDEX] + quantity,
+            )
+            update_product(storage, product_id, new_product)
+
+            if quantity == quantity_cart:
+                cart.pop(i)
+                return (product_id, 0)
+
+            cart[i] = (product_id, quantity_cart - quantity)
+
+            return cart[i]
+
+    return None
diff --git a/src/part2/crud.py b/src/part2/crud.py
index d026cbcb..3fc9ab49 100644
--- a/src/part2/crud.py
+++ b/src/part2/crud.py
@@ -1,79 +1,46 @@
-"""Create/read/update/delete operations over the in-memory product store.
-
-Every operation takes the store -- a list of
-:data:`~src.part2.storage.Product` tuples -- as its first argument and
-works on it in place. The failure path never raises: the operation prints
-an explanatory message to stdout and returns ``None``.
-
-The identifier of a new product is derived from the store itself
-(:func:`generate_product_id`): one past the greatest identifier in use, or
-:data:`~src.part2.storage.PRODUCT_ID_MIN` when the store is empty.
-Product names are kept unique -- :func:`create_product` refuses a name that
-is already taken.
-"""
-
 from decimal import Decimal
 
-from .storage import (  # noqa: F401
+from .storage import (
     NAME_INDEX,
     PRODUCT_ID_INDEX,
     PRODUCT_ID_MIN,
     Product,
 )
-from .utils import normalize_price  # noqa: F401
+from .utils import normalize_price
 
 
 def generate_product_id(storage: list[Product]) -> int:
-    """Choose the identifier for the next product added to ``storage``.
+    if len(storage) == 0:
+        return PRODUCT_ID_MIN
+    mx = max(product[PRODUCT_ID_INDEX] for product in storage) + 1
 
-    Args:
-        storage: The product store to inspect.
-
-    Returns:
-        One past the greatest identifier currently held in ``storage``, or
-        :data:`~src.part2.storage.PRODUCT_ID_MIN` when ``storage`` is
-        empty.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    return mx
 
 
 def create_product(
     storage: list[Product], fields: tuple[str, Decimal, int]
 ) -> int | None:
-    """Append a new product to ``storage`` and return its new identifier.
+    for product in storage:
+        if product[NAME_INDEX] == fields[0]:
+            print(f"product name {product[NAME_INDEX]} is already taken.")
+            return None
 
-    Args:
-        storage: The product store to append to; modified in place on
-            success.
-        fields: A ``(name, price, quantity)`` tuple describing the product.
-            ``price`` is a :class:`~decimal.Decimal` amount and is rounded
-            to the stored money precision before it is saved.
+    product_id = generate_product_id(storage)
+    name, price, quantity = fields
+    new_product = (product_id, name, normalize_price(price), quantity)
 
-    Returns:
-        The identifier generated for the new product, or ``None`` when a
-        product with the same name already exists. In the ``None`` case
-        ``storage`` is left unchanged and a message naming the clashing
-        name is printed.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    storage.append(new_product)
 
+    return product_id
 
-def read_product(storage: list[Product], product_id: int) -> Product | None:
-    """Return the product stored under ``product_id``.
 
-    Args:
-        storage: The product store to search.
-        product_id: The identifier to look up.
+def read_product(storage: list[Product], product_id: int) -> Product | None:
+    for product in storage:
+        if product[PRODUCT_ID_INDEX] == product_id:
+            return product
 
-    Returns:
-        The matching ``(product_id, name, price, quantity)`` record, or
-        ``None`` when no product carries that identifier (a message is
-        printed in that case).
-    """
-    # TODO: реализуйте функцию
-    return (0, "", Decimal(0), 0)
+    print(f"no product with id <{product_id}>")
+    return None
 
 
 def update_product(
@@ -81,40 +48,22 @@ def update_product(
     product_id: int,
     fields: tuple[str, Decimal, int],
 ) -> Product | None:
-    """Overwrite the fields of the product stored under ``product_id``.
-
-    The identifier itself is preserved; only ``name``, ``price`` and
-    ``quantity`` are replaced.
+    for i in range(len(storage)):
+        if storage[i][PRODUCT_ID_INDEX] == product_id:
+            name, price, quality = fields
+            new_product = (product_id, name, normalize_price(price), quality)
+            storage[i] = new_product
+            return new_product
 
-    Args:
-        storage: The product store to modify; the matching record is
-            replaced in place on success.
-        product_id: The identifier of the product to change.
-        fields: A ``(name, price, quantity)`` tuple with the new values.
-            ``price`` is a :class:`~decimal.Decimal` amount and is rounded
-            to the stored money precision before it is saved.
-
-    Returns:
-        The updated ``(product_id, name, price, quantity)`` record, or
-        ``None`` when no product carries that identifier (``storage`` is
-        left unchanged and a message is printed).
-    """
-    # TODO: реализуйте функцию
-    return (0, "", Decimal(0), 0)
+    print(f"no product with id <{product_id}>")
+    return None
 
 
 def delete_product(storage: list[Product], product_id: int) -> int | None:
-    """Remove the product stored under ``product_id`` from ``storage``.
-
-    Args:
-        storage: The product store to remove from; modified in place on
-            success.
-        product_id: The identifier of the product to remove.
-
-    Returns:
-        ``product_id`` when a product was removed, or ``None`` when no
-        product carried that identifier (``storage`` is left unchanged and
-        a message is printed).
-    """
-    # TODO: реализуйте функцию
-    return 0
+    for product in storage:
+        if product[PRODUCT_ID_INDEX] == product_id:
+            storage.remove(product)
+            return product_id
+
+    print(f"no product with id <{product_id}>")
+    return None
diff --git a/src/part2/storage.py b/src/part2/storage.py
index b63d5fc7..03128124 100644
--- a/src/part2/storage.py
+++ b/src/part2/storage.py
@@ -1,34 +1,14 @@
-"""In-memory product store for the shop CRUD exercise.
-
-The store is deliberately primitive: a plain list of tuples, with no
-persistence, no indexing and no schema enforcement. Each element is a
-:data:`Product` record -- a ``(product_id, name, price, quantity)`` tuple
-where:
-
-* ``product_id`` -- unique positive integer key, assigned by the create
-  operation in :mod:`src.part2.crud`;
-* ``name`` -- human-readable product name, unique across the store;
-* ``price`` -- price of a single unit, held as a :class:`~decimal.Decimal`
-  amount rounded to a fixed number of decimal places (see
-  :func:`src.part2.utils.normalize_price`) so that money is never
-  subject to binary floating-point error;
-* ``quantity`` -- number of units currently in stock.
-
-Field positions are exposed as ``*_INDEX`` constants so callers never
-hard-code tuple offsets.
-"""
-
 from decimal import Decimal
 from typing import Final
 
 
 type Product = tuple[int, str, Decimal, int]
 
-# TODO: задайте позиции полей внутри кортежа Product
+
 PRODUCT_ID_INDEX: Final = 0
-NAME_INDEX: Final = 0
-PRICE_INDEX: Final = 0
-QUANTITY_INDEX: Final = 0
+NAME_INDEX: Final = 1
+PRICE_INDEX: Final = 2
+QUANTITY_INDEX: Final = 3
+
 
-# TODO: задайте идентификатор первого товара в пустом хранилище
-PRODUCT_ID_MIN: Final[int] = 0
+PRODUCT_ID_MIN: Final[int] = 1
diff --git a/src/part2/utils.py b/src/part2/utils.py
index ec0348d3..659d1d07 100644
--- a/src/part2/utils.py
+++ b/src/part2/utils.py
@@ -1,29 +1,12 @@
-"""Standalone helpers shared by the hw4 storage and CRUD modules.
-
-For now this is limited to money handling: :func:`normalize_price` rounds a
-raw :class:`~decimal.Decimal` amount to the fixed number of fractional
-digits (:data:`PRICE_PRECISION`) that every stored price uses, keeping
-currency values free of binary floating-point error.
-"""
-
-from decimal import ROUND_HALF_UP, Decimal  # noqa: F401
+from decimal import ROUND_HALF_UP, Decimal
 from typing import Final
 
 
-# TODO: задайте число знаков после запятой и шаг квантования
-PRICE_PRECISION: Final[int] = 0
-PRICE_STEP: Final = Decimal(0)
+PRICE_PRECISION: Final[int] = 2
+PRICE_STEP: Final = Decimal(1).scaleb(-PRICE_PRECISION)
 
 
 def normalize_price(price: Decimal) -> Decimal:
-    """Round a price to the precision every stored record uses.
-
-    Args:
-        price: The raw price amount.
+    correct_price = price.quantize(PRICE_STEP, rounding=ROUND_HALF_UP)
 
-    Returns:
-        ``price`` quantised to :data:`PRICE_PRECISION` fractional digits,
-        with halves rounded up.
-    """
-    # TODO: реализуйте функцию
-    return Decimal(0)
+    return correct_price