#include <bits/stdc++.h>
using namespace std;
const int inf = (int)1e9;
const double INF = 1e12, EPS = 1e-9;
const int mod = (int)1e9 + 7;
int n, k;
string s;
int dp[2010][2010], sum[2010];
int main() {
  cin >> n >> k >> s;
  dp[0][0] = sum[0] = 1;
  for (int i = 0; i < (int)n; i++) {
    for (int j = 0; j < (int)k + 1; j++) {
      (dp[i + 1][j] += (long long)sum[j] * (s[i] - 'a') % mod) %= mod;
      for (int l = 0; i >= l && j >= (1 + l) * (n - i); l++) {
        (dp[i + 1][j] += (long long)dp[i - l][j - (1 + l) * (n - i)] *
                         ('z' - s[i]) % mod) %= mod;
      }
      (sum[j] += dp[i + 1][j]) %= mod;
    }
  }
  cout << sum[k] << endl;
  return 0;
}
