#include <bits/stdc++.h>
using namespace std;
void err(istream_iterator<string> it) {}
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << " = " << a << '\n';
  err(++it, args...);
}
template <class T1, class T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &a) {
  return os << '(' << a.first << ", " << a.second << ')';
}
template <class T>
ostream &operator<<(ostream &os, const vector<T> &a) {
  os << '[';
  for (unsigned int i = 0; i < a.size(); i++)
    os << a[i] << (i < a.size() - 1 ? ", " : "");
  os << ']';
  return os;
}
template <class T>
ostream &operator<<(ostream &os, const set<T> &a) {
  os << '{';
  for (typename set<T>::iterator it = a.begin(); it != a.end(); it++) {
    typename set<T>::iterator jt = it;
    os << *it << (++jt != a.end() ? ", " : "");
  }
  os << '}';
  return os;
}
template <class T1, class T2>
ostream &operator<<(ostream &os, map<T1, T2> &a) {
  os << "{\n";
  for (typename map<T1, T2>::iterator it = a.begin(); it != a.end(); it++) {
    typename map<T1, T2>::iterator jt = it;
    os << "  " << it->first << ": " << it->second
       << (++jt != a.end() ? ",\n" : "\n");
  }
  os << '}';
  return os;
}
const int mod = 1e9 + 7;
int n, k;
int dp[2005][2005];
int sum[2005][2005];
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> k;
  string s;
  cin >> s;
  s = "!" + s;
  sum[0][0] = 1;
  dp[0][0] = 1;
  for (int i = 1; i <= n + 1; i++) {
    if (i == n + 1) {
      dp[i][k] = sum[i - 1][k];
      continue;
    }
    for (int j = 0; j <= k; j++) {
      dp[i][j] = (dp[i][j] + sum[i - 1][j] * 1LL * (s[i] - 'a')) % mod;
      for (int k = i; k >= 1; k--) {
        int len = (i - k + 1);
        int more = len * 1LL * (n - i + 1);
        if (more > j) break;
        dp[i][j] = (dp[i][j] + dp[k - 1][j - more] * 1LL * ('z' - s[i])) % mod;
      }
      sum[i][j] = (dp[i][j] + sum[i - 1][j]) % mod;
    }
  }
  cout << dp[n + 1][k] << '\n';
}
