#include <bits/stdc++.h>
using namespace std;
const int P = 1e9 + 7, INF = 0x3f3f3f3f;
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
long long qpow(long long a, long long n) {
  long long r = 1 % P;
  for (a %= P; n; a = a * a % P, n >>= 1)
    if (n & 1) r = r * a % P;
  return r;
}
long long inv(long long first) {
  return first <= 1 ? 1 : inv(P % first) * (P - P / first) % P;
}
inline int rd() {
  int first = 0;
  char p = getchar();
  while (p < '0' || p > '9') p = getchar();
  while (p >= '0' && p <= '9') first = first * 10 + p - '0', p = getchar();
  return first;
}
const int N = 2e3 + 10;
int n, k, f[N][N], g[N][N];
char s[N];
inline void add(int &a, int b) {
  a += b;
  if (a >= P) a -= P;
}
int main() {
  scanf("%d%d%s", &n, &k, s + 1);
  int ans = 0;
  for (int i = 1; i <= n + 1; ++i) f[i][0] = 1;
  for (int i = n; i >= 0; --i)
    for (int j = 0; j <= k; ++j) {
      int &r = f[i + 1][j];
      add(r, g[i][j] = g[i + 1][j]);
      if (!r) continue;
      if (!i) {
        if (j == k) add(ans, r);
        continue;
      }
      if (s[i] != 'a') {
        int first = (long long)(s[i] - 'a') * r % P;
        add(g[i][j], first);
      }
      if (s[i] != 'z') {
        int first = (long long)('z' - s[i]) * r % P;
        int d = n - i + 1, now = j + d;
        if (now > k) continue;
        for (int t = i; t >= 1; --t) {
          add(f[t][now], first);
          if ((now += d) > k) break;
        }
      }
    }
  printf("%d\n", ans);
}
