#include <bits/stdc++.h>
using ll = long long;
const int C = 2001, M = 1000000007;
ll dp[C][C], equal[C][C];
int main() {
  std::string a;
  int k, ln, i, j, ij, x;
  std::cin >> ln >> k >> a;
  dp[0][0] = a[0] - 'a';
  equal[0][0] = 1;
  i = 0, j = 0;
  for (ij = 0, x = ln - i; i + ij < ln && j + (ij + 1) * x <= k; ij++, x--) {
    dp[i + ij][j + (ij + 1) * x] += ('z' - a[i + ij]);
    dp[i + ij][j + (ij + 1) * x] %= M;
  }
  if (i + ij < ln) {
    for (ij = ln - i - 1, x = 1; ij > 0 && j + (ij + 1) * x <= k; ij--, x++) {
      dp[i + ij][j + (ij + 1) * x] += ('z' - a[i + ij]);
      dp[i + ij][j + (ij + 1) * x] %= M;
    }
  }
  for (i = 1; i < ln; i++) {
    for (j = 0; j <= k; j++) {
      equal[i][j] = (dp[i - 1][j] + equal[i - 1][j]) % M;
      dp[i][j] =
          (dp[i][j] + (dp[i - 1][j] + equal[i - 1][j]) * (a[i] - 'a')) % M;
      for (ij = 0, x = ln - i; i + ij < ln && j + (ij + 1) * x <= k;
           ij++, x--) {
        dp[i + ij][j + (ij + 1) * x] += dp[i - 1][j] * ('z' - a[i + ij]);
        dp[i + ij][j + (ij + 1) * x] %= M;
      }
      if (i + ij < ln) {
        for (ij = ln - i - 1, x = 1; ij > 0 && j + (ij + 1) * x <= k;
             ij--, x++) {
          dp[i + ij][j + (ij + 1) * x] += dp[i - 1][j] * ('z' - a[i + ij]);
          dp[i + ij][j + (ij + 1) * x] %= M;
        }
      }
    }
  }
  printf("%lld\n", (dp[ln - 1][k] + equal[ln - 1][k]) % M);
  return 0;
}
