#include <bits/stdc++.h>
using namespace std;
const int M = 2000 + 5;
long long int dp[M][M];
long long int pre[M][M];
long long int mod = 1000000007;
int main() {
  time_t t_start, t_end;
  t_start = clock();
  int n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  dp[0][0] = 1;
  pre[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j <= k; j++) {
      long long int s1 = 0;
      for (int l = max(0, i - j / (n - i + 1)); l <= i - 1; l++) {
        s1 = s1 + dp[l][j - (i - l) * (n - i + 1)];
        s1 = s1 % mod;
      }
      s1 = s1 * ('z' - s[i - 1]);
      s1 = s1 % mod;
      long long int s2 = 0;
      s2 = pre[i - 1][j];
      s2 = s2 * (s[i - 1] - 'a');
      s2 = s2 % mod;
      long long int s3 = (s1 + s2) % mod;
      dp[i][j] = s3;
      pre[i][j] = (pre[i - 1][j] + s3) % mod;
    }
  }
  long long int ans = 0;
  for (int i = 0; i <= n; i++) {
    ans = ans + dp[i][k];
    ans = ans % mod;
  }
  cout << ans << endl;
  t_end = clock();
  return 0;
}
