#include <bits/stdc++.h>
using namespace std;
long long n, k, ways[2100][2100][3];
string st;
long long shf[25000];
long long temp;
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n >> k;
  cin >> st;
  ways[n + 1][0][1] = 1;
  shf[0] = 1;
  for (int i = n; i; --i) {
    for (int calc = 0; calc <= 2000; calc++) {
      ways[i][calc][0] =
          1ll * (st[i - 1] - 'a') *
          (ways[i + 1][calc][2] + ways[i + 1][calc][1] + ways[i + 1][calc][0]) %
          1000000007;
      temp = n - i + 1;
      temp = calc - temp;
      if (temp >= 0)
        ways[i][calc][2] = 1ll * ('z' - st[i - 1]) *
                           (ways[i + 1][temp][0] + ways[i + 1][temp][1] +
                            ways[i + 1][temp][2]) %
                           1000000007;
      ways[i][calc][1] += shf[calc];
      ways[i][calc][1] %= 1000000007;
      for (int q = i - 1; q >= 1; --q) {
        temp = (i - q) * (n - i + 1);
        if (temp + calc > 2000) break;
        ways[q][temp + calc][1] += ways[i][calc][2];
      }
    }
    for (int calc = 0; calc <= 2000; calc++)
      shf[calc] = (shf[calc] + ways[i][calc][0]) % 1000000007;
  }
  cout << (ways[1][k][0] + ways[1][k][1] + ways[1][k][2]) % 1000000007 << endl;
  cin.get();
  cin.get();
  return 0;
}
