#include <bits/stdc++.h>
using namespace std;
long long dp[2050][2050];
long long p[2050][2050];
const int mod = 1e9 + 7;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  s = " " + s;
  dp[0][0] = 1;
  p[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    for (int sum = 0; sum <= k; sum++) {
      dp[i][sum] = (dp[i][sum] + p[i - 1][sum] * (s[i] - 'a')) % mod;
      for (int pref = 0; pref < i; pref++) {
        if (sum - (1 + pref) * (n - i + 1) >= 0) {
          dp[i][sum] =
              (dp[i][sum] + dp[i - pref - 1][sum - (1 + pref) * (n - i + 1)] *
                                ('z' - s[i])) %
              mod;
        } else {
          break;
        }
      }
    }
    for (int sum = 0; sum <= k; sum++) {
      p[i][sum] = (dp[i][sum] + p[i - 1][sum]) % mod;
    }
  }
  cout << p[n][k];
}
