Author:  A. Klenin  Time limit:  2 sec  
Input file:  input.txt  Memory limit:  256 Mb  
Output file:  output.txt 
The height map of some square country is represented with a matrix of N × N integers. Each integer reflects average height of the corresponding area. We will denote the height value at location (x, y) as h[x, y].
A location (x, y) is named depression if for all x′ = x − W… x + W, y′ = y − W… y + W location (x′, y′) is also inside of the map and h[x, y] ≤ h[x′,y′].
Your program must find coordinates of all depressions of the given height map.
Input file contains integers N W, followed by N × N integers — location heights, rowbyrow.
Output file must contain an integer M — number of possible depressions, followed by M pairs of integers x_{i} y_{i}, where x_{i} — the column of the ith depression, y_{i} — the row of the ith depression. Numbering starts from 1.
Depressions must be ordered by y, then by x.
3 ≤ N ≤ 500
1 ≤ W
2 × W < N
1 ≤ h[x, y] ≤ 1000
No.  Input file (input.txt ) 
Output file (output.txt ) 

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