#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e3 + 7;
const long long md = 1e9 + 7;
long long dp[maxn][maxn];
long long pref[maxn];
int main() {
  int n, K;
  scanf("%d", &n);
  scanf("%d", &K);
  string s;
  cin >> s;
  s = " " + s;
  for (int j = 0; j < maxn; j++) {
    dp[0][j] = pref[j] = 0;
  }
  dp[0][0] = pref[0] = 1;
  for (int i = 1; i <= n; i++) {
    for (int k = 0; k <= K; k++) {
      dp[i][k] = pref[k] * ((int)(s[i] - 'a'));
      int cur = n - i + 1;
      for (int p = 1; (p * cur <= k) && (p <= i); p++) {
        dp[i][k] = dp[i][k] + dp[i - p][k - p * cur] * ((int)('z' - s[i]));
      }
      dp[i][k] %= md;
      pref[k] = (pref[k] + dp[i][k]) % md;
    }
  }
  printf("%lld", pref[K]);
  printf("\n");
}
