#include <bits/stdc++.h>
using namespace std;
const int inf = 1e9 + 7;
template <class T>
void dbs(string str, T t) {
  cerr << str << " : " << t << "\n";
}
template <class T, class... second>
void dbs(string str, T t, second... s) {
  int idx = str.find(',');
  cerr << str.substr(0, idx) << " : " << t << ", ";
  dbs(str.substr(idx + 1), s...);
}
template <class second, class T>
ostream& operator<<(ostream& os, const pair<second, T>& p) {
  return os << "(" << p.first << ", " << p.second << ")";
}
template <class T>
void prc(T a, T b) {
  cerr << "[";
  for (T i = a; i != b; ++i) {
    if (i != a) cerr << ", ";
    cerr << *i;
  }
  cerr << "]\n";
}
const int N = 2020;
long long first[N][N];
long long G[N][N];
string s;
long long g(int n, int k);
long long f(int n, int k) {
  if (k < 0) return 0;
  if (n == 0) return k == 0;
  long long& ans = first[n][k];
  if (ans != -1) return ans;
  ans = 0;
  int ch = s[int(s.size()) - n] - 'a';
  ans = ch * f(n - 1, k) + (25 - ch) * f(n - 1, k - n) + g(n - 1, k) + (k == 0);
  int nk = k;
  for (int i = 1; i <= n - 1; ++i) {
    int ch = s[int(s.size()) - n + i] - 'a';
    nk = k - (i + 1) * (n - i);
    if (nk < 0) {
      for (int i = n - 1; i >= 1; --i) {
        int ch = s[int(s.size()) - n + i] - 'a';
        nk = k - (i + 1) * (n - i);
        if (nk < 0) break;
        ans += (25 - ch) * f(n - i - 1, nk);
        ans %= inf;
      }
      break;
    }
    ans += (25 - ch) * f(n - i - 1, nk);
    ans %= inf;
  }
  ans %= inf;
  return ans;
}
long long g(int n, int k) {
  if (k < 0) return 0;
  if (n == 0) return 0;
  long long& ans = G[n][k];
  if (ans != -1) return ans;
  int ch = s[int(s.size()) - n] - 'a';
  ans = ch * f(n - 1, k) + g(n - 1, k);
  ans %= inf;
  return ans;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  memset(first, -1, sizeof first);
  memset(G, -1, sizeof G);
  cin >> s;
  cout << f(n, k) << "\n";
  return 0;
}
