#include <bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:102400000,102400000")
const int MOD = 1e9 + 7;
const int N = 2007;
int n, k;
char s[N];
long long f[N][N], g[N][N];
int main() {
  scanf("%d%d", &n, &k);
  scanf("%s", s + 1);
  f[0][0] = 1;
  g[0][0] = 1;
  for (int i = int(1); i <= int(n); ++i) {
    for (int j = int(0); j <= int(k); ++j) {
      f[i][j] = g[i - 1][j] * (s[i] - 'a') % MOD;
      f[i][j] %= MOD;
      for (int l = 1; l <= i && l * (n + 1 - i) <= j; ++l) {
        f[i][j] += f[i - l][j - l * (n + 1 - i)] * ('z' - s[i]) % MOD;
        f[i][j] %= MOD;
      }
      g[i][j] = (g[i - 1][j] + f[i][j]) % MOD;
    }
  }
  cout << g[n][k] << endl;
  return 0;
}
