#include <bits/stdc++.h>
using namespace std;
const int maxn = 2005, mod = 1e9 + 7;
long long dp[2005][2005], ssum[2005][2005];
char str[2005];
int main() {
  int i, j, t, n, k;
  scanf("%d%d%s", &n, &k, str + 1);
  dp[1][n] = 'z' - str[1];
  dp[1][0] = str[1] - 'a';
  ssum[1][n] = dp[1][n];
  ssum[1][0] = dp[1][0];
  for (i = 2; i <= n; ++i) {
    for (j = 0; j <= k; ++j) {
      dp[i][j] += ssum[i - 1][j] * (str[i] - 'a');
      dp[i][j] %= mod;
    }
    for (t = i - 1; t >= 1; --t) {
      int base = (i - t) * (n - i + 1);
      for (j = base; j <= k; ++j) {
        dp[i][j] += dp[t][j - base] * ('z' - str[i]);
        dp[i][j] %= mod;
      }
    }
    dp[i][0] += str[i] - 'a';
    if (i * (n - i + 1) <= k) dp[i][i * (n - i + 1)] += 'z' - str[i];
    for (j = 0; j <= k; ++j) ssum[i][j] = (ssum[i - 1][j] + dp[i][j]) % mod;
  }
  for (j = 0; j <= k; ++j) {
    dp[n][j] += ssum[n - 1][j];
    dp[n][j] %= mod;
  }
  dp[n][0]++;
  dp[n][0] %= mod;
  printf("%I64d\n", dp[n][k]);
  return 0;
}
