#include <bits/stdc++.h>
using namespace std;
const long long BBP = 1e9 + 7;
int n, k;
long long d[2001][2005], sum[2005];
string s;
int main() {
  cin >> n >> k;
  cin >> s;
  d[0][0] = 1;
  sum[0] = 1;
  for (int i = 1; i <= n; ++i) {
    for (int j = 0; j <= k; ++j) {
      d[i][j] = (sum[j] * (int(s[i - 1]) - int('a'))) % BBP;
      int c = i - 1;
      while (c > 0 && (i - c) * (n - i + 1) <= j) {
        long long hz = (i - c) * (n - i + 1);
        d[i][j] = (d[i][j] + d[c][j - hz] * (int('z') - int(s[i - 1]))) % BBP;
        --c;
      }
      if (i * (n - i + 1) == j) {
        d[i][j] = (d[i][j] + (int('z') - int(s[i - 1]))) % BBP;
      }
      sum[j] = (sum[j] + d[i][j]) % BBP;
    }
  }
  long long ans = 0;
  for (int i = 0; i <= n; ++i) {
    ans = (ans + d[i][k]) % BBP;
  }
  cout << ans;
  return 0;
}
