#include <bits/stdc++.h>
using namespace std;
int N, K;
char s[2001];
unsigned int M[2001][2001], aux, A[2001];
int main() {
  scanf("%d%d", &(N), &(K));
  scanf("%s", &s);
  M[N][0] = 1;
  A[0] = 1;
  for (int i = N - 1; i >= 0; i--) {
    for (int k = 0; k <= K; k++)
      if (M[i + 1][k]) {
        aux = ((long long)(s[i] - 'a') * M[i + 1][k]) % 1000000007;
        M[i][k] = (M[i][k] + A[k] + aux) % 1000000007;
        A[k] = (A[k] + aux) % 1000000007;
        aux = ((long long)('z' - s[i]) * M[i + 1][k]) % 1000000007;
        if (aux)
          for (int j = i, p = N - i; j >= 0 && k + p <= K; j--, p += N - i)
            M[j][k + p] = (M[j][k + p] + aux) % 1000000007;
      }
  }
  cout << M[0][K] << endl;
}
