#include <bits/stdc++.h>
using namespace std;
const int Mod = 1e9 + 7;
const int maxn = 2e3 + 100;
int n, k, f[maxn][maxn], pref[maxn];
char s[maxn];
void Enter() {
  cin >> n >> k;
  for (int i = 1; i <= n; ++i) cin >> s[i];
}
void Init() {}
void Solve() {
  pref[0] = 1;
  f[0][0] = 1;
  for (int i = 1; i <= n; ++i)
    for (int j = 0; j <= k; ++j) {
      f[i][j] = 1ll * pref[j] * (s[i] - 'a') % Mod;
      for (int i2 = i - 1; i2 >= 0 && (i - i2) * (n - i + 1) <= j; --i2)
        f[i][j] =
            (f[i][j] + 1ll * f[i2][j - (i - i2) * (n - i + 1)] * ('z' - s[i])) %
            Mod;
      pref[j] = (pref[j] + f[i][j]) % Mod;
    }
  cout << pref[k];
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  Enter();
  Init();
  Solve();
}
