#include <bits/stdc++.h>
using namespace std;
const int MOD = 1000000007;
const int MAX_N = 2010;
const int MAX_K = 2010;
int n, k, sol;
long long dp[MAX_N][MAX_K], sum[MAX_N][MAX_K];
char str[MAX_N];
int main() {
  cin >> n >> k;
  cin >> (str + 1);
  dp[0][0] = 1;
  sol = dp[0][k];
  for (int i = 1; i <= n; ++i) {
    for (int j = 0; j <= k; ++j) {
      for (int step = 1; step <= i && j - step * (n - i + 1) >= 0; ++step) {
        dp[i][j] =
            (dp[i][j] + dp[i - step][j - step * (n - i + 1)] * ('z' - str[i])) %
            MOD;
      }
      sum[i][j] = (sum[i - 1][j] + dp[i - 1][j]) % MOD;
      dp[i][j] = (dp[i][j] + sum[i][j] * (str[i] - 'a')) % MOD;
    }
    sol = (sol + dp[i][k]) % MOD;
  }
  cout << sol << endl;
  return 0;
}
