diff --git "a/leetcode3/\354\227\274\355\230\234\354\240\225/3827. Count Monobit Integers.java" "b/leetcode3/\354\227\274\355\230\234\354\240\225/3827. Count Monobit Integers.java"
new file mode 100644
index 00000000..438d7e45
--- /dev/null
+++ "b/leetcode3/\354\227\274\355\230\234\354\240\225/3827. Count Monobit Integers.java"	
@@ -0,0 +1,14 @@
+// 0을 제외하고 1, 11, 111, 1111... (2^1 - 1, 2^2 - 1, 2^3 -1)
+// o(log n)
+
+class Solution {
+    public int countMonobit(int n) {
+        int cnt = 1; // 0은 무조건 포함
+        int num = 1;
+        while (num <= n) {
+            cnt++;
+            num = num * 2 + 1;
+        }
+        return cnt;
+    }
+}