Count Islands

Given a 2D grid of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. Use BFS or DFS to explore and mark visited cells. Example: 11110 11010 11000 00000 → 1 island

Input

Line 1: m n (rows and columns). Next m lines: strings of 0s and 1s.

Output

The number of islands.

Sample

4 5
11110
11010
11000
00000

Expected

1