#include <bits/stdc++.h>
const double eps = 1e-9;
const long double pi = acos(-1.0);
using namespace std;
const int N = 2e3 + 3;
long long dp[N][N], g[N][N];
const long long MOD = 1e9 + 7;
void solve() {
  string s;
  int n, k;
  cin >> n >> k;
  cin >> s;
  dp[0][0] = 1;
  g[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    for (int sum = 0; sum <= k; sum++) {
      dp[i][sum] += g[i - 1][sum] * (s[i - 1] - 'a');
      dp[i][sum] %= MOD;
      for (int pref = 0; pref <= i - 1; pref++) {
        int q = i - pref - 1;
        if (sum - (pref + 1) * (n - i + 1) < 0) break;
        dp[i][sum] += dp[q][sum - (pref + 1) * (n - i + 1)] * ('z' - s[i - 1]);
        dp[i][sum] %= MOD;
      }
      g[i][sum] = g[i - 1][sum] + dp[i][sum];
      g[i][sum] %= MOD;
    }
  }
  long long ans = 0;
  cout << g[n][k] << endl;
}
int main() {
  ios::sync_with_stdio(NULL), cin.tie(0), cout.tie(0);
  cout.setf(ios::fixed), cout.precision(10);
  int step;
  step = 1;
  for (int i = 1; i <= step; i++) {
    solve();
  }
}
