#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-8;
const double pi = acos(-1.0);
int dblcmp(double d) {
  if (fabs(d) < eps) return 0;
  return d > eps ? 1 : -1;
}
const long long mod = 1000000007;
int n, d;
string s;
long long dp[2111][2111], sum[2111][2111];
long long p26[2111];
int main() {
  int i, j, k, cas;
  p26[0] = 1;
  for (i = 1; i < 2111; i++) {
    p26[i] = p26[i - 1] * 26;
    p26[i] %= mod;
  }
  cin >> n >> d >> s;
  memset((dp), 0, sizeof(dp));
  memset((sum), 0, sizeof(sum));
  dp[0][0] = 1;
  sum[0][0] = 1;
  for (i = 1; i <= n; i++) {
    for (j = 0; j <= d; j++) {
      long long st = sum[i - 1][j];
      dp[i][j] += st * (s[i - 1] - 'a') % mod;
      dp[i][j] %= mod;
      for (k = i - 1; k >= 0; k--) {
        if (j - (n - i + 1) * (i - k) >= 0) {
          dp[i][j] += dp[k][j - (n - i + 1) * (i - k)] * ('z' - s[i - 1]) % mod;
          dp[i][j] %= mod;
        } else
          break;
      }
      sum[i][j] = sum[i - 1][j] + dp[i][j];
      sum[i][j] %= mod;
    }
  }
  long long ans = 0;
  for (i = 0; i <= n; i++) {
    ans += dp[i][d];
    ans %= mod;
  }
  cout << ans << endl;
  return 0;
}
