#include <iostream>
#include <fstream>

using namespace std;

ifstream fin  ("matrix.in");
ofstream fout ("matrix.out");

char lit, car;
int n, m, sol;
int s[1005][1005][130], virus[130];
bool ok;


int main (){
      fin>>n>>m;
      for(int i=1; i<=n; i++)
            for(int j=1; j<=n; j++){
                  fin>>car;
                  for(int c='a'; c<='z'; c++)
                        s[i][j][c]=s[i-1][j][c] + s[i][j-1][c] - s[i-1][j-1][c];

                  s[i][j][car]++;
            }

      for(int i=m+1; i<=n; i++)
            for(int j=m+1; j<=n; j++){
                  ok=1;
                  for(int c='a'; c<='z'; c++)
                        if(s[i][j][c] - s[i-m][j][c] - s[i][j-m][c] + s[i-m][j-m][c] != virus[c])
                              ok=0;
                  sol+=ok;
            }

      fout<<sol;
      return 0;
}