#include <bits/stdc++.h>
using namespace std;
inline long long sqr(long long x) { return x * x; }
const long long base = 1e9 + 7;
int n, k;
char s[2005];
long long dp[2005][2005], col[2005];
int main() {
  scanf("%d%d%s", &n, &k, s + 1);
  dp[0][0] = col[0] = 1;
  for (int i = (1), _b = (n); i <= _b; ++i) {
    int c = s[i] - 'a';
    for (int j = (0), _b = (k); j <= _b; ++j) {
      dp[i][j] = col[j] * (long long)c;
      for (int x = (1), _b = (i); x <= _b; ++x) {
        if (x * (n - i + 1) > j) break;
        dp[i][j] =
            (dp[i][j] +
             (dp[i - x][j - x * (n - i + 1)] * (long long)(25 - c)) % base) %
            base;
      }
      col[j] = (col[j] + dp[i][j]) % base;
    }
  }
  printf("%I64d", col[k]);
  return 0;
}
