Find Largest House Area

In the grid, 1 represents a roof and 0 represents open ground. Only 1s adjacent up, down, left or right belong to the same house; diagonal cells are not connected. Find the number of cells covered by the largest house.

The original problem's connectivity rule is clear; this site adds the grid size and the result for a grid with no houses.

输入格式

The first line contains n m (1≤n,m, and nm≤200000); each of the next n lines contains m values, each 0 or 1.

输出格式

Output the area of the largest connected component; output 0 if there is no 1.

样例 1

输入：

4 3
0 0 0
0 1 1
0 0 0
1 1 0

输出：

2

样例 2

输入：

2 2
1 0
0 1

输出：

1

样例 3

输入：

1 1
0

输出：

0