#include <bits/stdc++.h>
using namespace std;
const int Mod = (int)1e9 + 7;
long long dp[2005][2005];
long long sum[2005];
char str[2005];
int main() {
  int n, K;
  scanf("%d%d", &n, &K);
  scanf("%s", str + 1);
  dp[0][0] = sum[0] = 1;
  for (int i = (1), _t = (n); i <= _t; ++i) {
    for (int j = (i - 1), _t = (0); j >= _t; --j) {
      if ((i - j) * (n - i + 1) > K) break;
      for (int k = ((i - j) * (n - i + 1)), _t = (K); k <= _t; ++k) {
        dp[i][k] =
            (dp[i][k] + dp[j][k - (i - j) * (n - i + 1)] * ('z' - str[i])) %
            Mod;
      }
    }
    for (int j = (0), _t = (K); j <= _t; ++j)
      dp[i][j] = (dp[i][j] + sum[j] * (str[i] - 'a')) % Mod;
    for (int j = (0), _t = (K); j <= _t; ++j)
      sum[j] = (sum[j] + dp[i][j]) % Mod;
  }
  printf("%lld\n", sum[K]);
  return 0;
}
