#include <bits/stdc++.h>
using namespace std;
template <typename T>
inline bool upmin(T &x, T y) {
  return y < x ? x = y, 1 : 0;
}
template <typename T>
inline bool upmax(T &x, T y) {
  return x < y ? x = y, 1 : 0;
}
const long double eps = 1e-11;
const long double pi = acos(-1);
const int oo = 1 << 30;
const long long loo = 1ll << 62;
const int mods = 1e9 + 7;
const int MAXN = 2005;
const int INF = 0x3f3f3f3f;
inline int read() {
  int f = 1, x = 0;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') f = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    x = (x << 3) + (x << 1) + (c ^ 48);
    c = getchar();
  }
  return x * f;
}
char st[MAXN];
int f[MAXN][MAXN], sum[MAXN];
signed main() {
  int n = read(), k = read();
  scanf("%s", st + 1);
  f[0][0] = 1, sum[0] = 1;
  for (int i = 1; i <= n; i++)
    for (int j = 0; j <= k; j++) {
      for (int t = i - 1; t >= 0 && (n - i + 1) * (i - t) <= j; t--)
        (f[i][j] +=
         1ll * f[t][j - (n - i + 1) * (i - t)] * ('z' - st[i]) % mods) %= mods;
      (f[i][j] += 1ll * sum[j] * (st[i] - 'a') % mods) %= mods;
      (sum[j] += f[i][j]) %= mods;
    }
  int ans = 0;
  for (int i = 0; i <= n; i++) (ans += f[i][k]) %= mods;
  printf("%d\n", ans);
  return 0;
}
