#include <bits/stdc++.h>
using namespace std;
int n, k;
char C[3000];
long long D[3000][3000];
long long S[3000];
long long s = 0;
int main() {
  cin >> n >> k;
  cin >> C;
  S[0] = D[0][0] = (C[0] - 'a');
  S[n] = D[0][n] = ('z' - C[0]);
  s = D[0][k];
  for (int i = 1; i < n; i++) {
    int z = (i + 1) * (n - i);
    D[i][0] += (C[i] - 'a');
    if (z <= k) D[i][z] += ('z' - C[i]);
    for (int j = 0; j < i; j++) {
      int z = (i - j) * (n - i);
      for (int x = z; x <= k; x++) D[i][x] += ('z' - C[i]) * D[j][x - z];
    }
    for (int j = 0; j <= k; j++) {
      D[i][j] += (C[i] - 'a') * S[j];
      D[i][j] %= 1000000007;
      S[j] += D[i][j];
      S[j] %= 1000000007;
    }
    s += D[i][k];
    s %= 1000000007;
  }
  if (k == 0) s++;
  cout << s % 1000000007 << endl;
  return 0;
}
