#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:36777216")
using namespace std;
int n, m;
long long f[2005][2005], sum[2005][2005];
char ch[2005];
int main() {
  cin >> n >> m;
  scanf(" %s", ch + 1);
  f[0][0] = 1;
  for (int i = 0; i <= n; i++) sum[i][0] = 1;
  for (int i = 1; i <= n; i++)
    for (int j = 0; j <= m; j++) {
      if (i != n)
        f[i][j] += sum[i - 1][j] * (ch[i] - 'a'), f[i][j] %= 1000000007;
      if (i == n)
        f[i][j] += sum[i - 1][j] * (ch[i] - 'a' + 1), f[i][j] %= 1000000007;
      for (int k = 0; j - (n - i + 1) * (k + 1) >= 0 && i - 1 - k >= 0; k++) {
        f[i][j] += f[i - 1 - k][j - (n - i + 1) * (k + 1)] * ('z' - ch[i]);
        f[i][j] %= 1000000007;
      }
      sum[i][j] = sum[i - 1][j] + f[i][j];
      sum[i][j] %= 1000000007;
    }
  cout << f[n][m] << endl;
}
