- Time limit: 2.00 s
- Memory limit: 512 MB
Count the number of rectangles whose each corner square is black.
Input
The first input line contains two integer $n$ and $m$: the size of the grid.
Then, there are $n$ lines of length $m$ that describe the grid. Each line consists of characters 0 (white) and 1 (black).
Output
Print the number of rectangles whose each corner square is black.
Constraints
- $1 \le n,m \le 3000$
Input:
3 4
0111
0011
0101
Output:
2