#include <bits/stdc++.h>
using namespace std;
int n, k, m;
int c[2005], o[2005], f[2005][2005];
string s;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> m >> s;
  for (int i = (0); i <= (s.length() - 1); i++) c[i] = s[i] - 'a';
  f[0][0] = 1;
  for (int i = (0); i <= (n); i++)
    for (int j = (0); j <= (m); j++) {
      (o[j] += f[i][j]) %= 1000000007;
      if (i < n && s[i] > 'a')
        (f[i + 1][j] += (1ll * c[i] * o[j]) % 1000000007) %= 1000000007;
      if (i < n && s[i] < 'z') {
        long long z = 25 - c[i];
        for (int k = i, e = n - i; k >= 0 && j + e <= m; k--, e += n - i)
          f[i + 1][j + e] = (f[i + 1][j + e] + z * f[k][j]) % 1000000007;
      }
    }
  cout << o[m];
  return 0;
}
