#include <bits/stdc++.h>
using namespace std;
const int MN = 2020;
const int MOD = 1000000007;
int dp[MN][MN];
int sum[MN][MN];
char s[MN];
int main() {
  int n, k;
  scanf("%d %d", &n, &k);
  scanf("%s", s);
  dp[0][0] = 1;
  sum[0][0] = 1;
  for (int i = 1; i <= n; ++i) {
    for (int j = 0; j <= k; ++j) {
      dp[i][j] += 1LL * sum[i - 1][j] * (s[i - 1] - 'a') % MOD;
      dp[i][j] %= MOD;
      for (int pre = 1; i - pre >= 0; ++pre) {
        if (j - pre * (n - i + 1) < 0) break;
        dp[i][j] +=
            1LL * dp[i - pre][j - pre * (n - i + 1)] * ('z' - s[i - 1]) % MOD;
        dp[i][j] %= MOD;
      }
      sum[i][j] += (dp[i][j] + sum[i - 1][j]) % MOD;
      sum[i][j] %= MOD;
    }
  }
  int ans = 0;
  for (int i = 0; i <= n; ++i) ans = (ans + dp[i][k]) % MOD;
  printf("%d\n", ans);
  return 0;
}
