#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e18 + 1;
inline long long input(void) {
  char t;
  long long x = 0;
  int neg = 0;
  t = getchar();
  while ((t < 48 || t > 57) && t != '-') t = getchar();
  if (t == '-') {
    neg = 1;
    t = getchar();
  }
  while (t >= 48 && t <= 57) {
    x = (x << 3) + (x << 1) + t - 48;
    t = getchar();
  }
  if (neg) x = -x;
  return x;
}
inline void output(long long x) {
  char a[20];
  int i = 0, j;
  a[0] = '0';
  if (x < 0) {
    putchar('-');
    x = -x;
  }
  if (x == 0) putchar('0');
  while (x) {
    a[i++] = x % 10 + 48;
    x /= 10;
  }
  for (j = i - 1; j >= 0; j--) {
    putchar(a[j]);
  }
  putchar('\n');
}
long long dp[2001][2001], n, pref[2002];
char s[2002];
int main() {
  long long k;
  n = input();
  k = input();
  scanf("%s", s + 1);
  memset(pref, 0, sizeof(pref));
  dp[0][0] = 1;
  pref[0] = 1;
  for (int i = 1; i < n + 1; ++i)
    for (int j = 0; j < k + 1; ++j) {
      dp[i][j] = pref[j] * (s[i] - 'a');
      if (i == n) dp[i][j] += pref[j];
      for (int prefix = 0; j >= (1 + prefix) * (n - i + 1) && prefix < i;
           prefix++)
        dp[i][j] +=
            dp[i - prefix - 1][j - (1 + prefix) * (n - i + 1)] * ('z' - s[i]);
      dp[i][j] %= 1000000007;
      pref[j] = (pref[j] + dp[i][j]) % 1000000007;
    }
  output(dp[n][k]);
  return 0;
}
