#include <bits/stdc++.h>
using namespace std;
template <typename T, typename U>
inline void smin(T &a, U b) {
  if (a > b) a = b;
}
template <typename T, typename U>
inline void smax(T &a, U b) {
  if (a < b) a = b;
}
template <class T>
inline void gn(T &first) {
  char c, sg = 0;
  while (c = getchar(), (c > '9' || c < '0') && c != '-')
    ;
  for ((c == '-' ? sg = 1, c = getchar() : 0), first = 0; c >= '0' && c <= '9';
       c = getchar())
    first = (first << 1) + (first << 3) + c - '0';
  if (sg) first = -first;
}
template <class T, class T1>
inline void gn(T &first, T1 &second) {
  gn(first);
  gn(second);
}
template <class T, class T1, class T2>
inline void gn(T &first, T1 &second, T2 &z) {
  gn(first);
  gn(second);
  gn(z);
}
template <class T>
inline void print(T first) {
  if (first < 0) {
    putchar('-');
    return print(-first);
  }
  if (first < 10) {
    putchar('0' + first);
    return;
  }
  print(first / 10);
  putchar(first % 10 + '0');
}
template <class T>
inline void printsp(T first) {
  print(first);
  putchar(' ');
}
template <class T>
inline void println(T first) {
  print(first);
  putchar('\n');
}
template <class T, class U>
inline void print(T first, U second) {
  printsp(first);
  println(second);
}
template <class T, class U, class V>
inline void print(T first, U second, V z) {
  printsp(first);
  printsp(second);
  println(z);
}
int power(int a, int b, int m, int ans = 1) {
  for (; b; b >>= 1, a = 1LL * a * a % m)
    if (b & 1) ans = 1LL * ans * a % m;
  return ans;
}
int main() {
  const int NN = 2020;
  static int dp[NN][NN], sum[NN][NN];
  static char s[NN];
  int n, k;
  gn(n, k);
  scanf("%s", s + 1);
  int ans = k == 0;
  dp[0][0] = 1;
  int pre = 1;
  for (int i = 1; i <= n; i++) {
    dp[i][0] = (long long)pre * (s[i] - 'a') % 1000000007;
    pre = (dp[i][0] + pre) % 1000000007;
    if (k == 0) ans = (ans + dp[i][0]) % 1000000007;
  }
  for (int j = 1; j <= k; j++) {
    int pre = 0;
    for (int i = 1; i <= n; i++) {
      dp[i][j] = (dp[i][j] + (long long)pre * (s[i] - 'a')) % 1000000007;
      long long mid = 0;
      const long long MOD1 = (long long)1000000007 * 1000000007;
      for (int r = 1; r <= i; r++) {
        if (j < r * (n - i + 1)) break;
        mid = (mid + (long long)dp[i - r][j - r * (n - i + 1)] * ('z' - s[i]));
        if (mid >= MOD1) mid -= MOD1;
      }
      dp[i][j] = (dp[i][j] + mid) % 1000000007;
      pre = (dp[i][j] + pre) % 1000000007;
      if (j == k) ans = (ans + dp[i][j]) % 1000000007;
    }
  }
  println(ans);
  return 0;
}
