#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  long long x = -1;
  for (long long i = 97; i <= 122; ++i) {
    char c = char(i);
    long long cnt = 0;
    for (long long i = 0; i < n; ++i) {
      if (s[i] == c) {
        long long c1 = 0;
        while (s[i] == c && c1 < k && i < n) {
          i++;
          c1++;
        }
        if (c1 == k) {
          cnt++;
          i--;
        }
      }
    }
    x = max(x, cnt);
  }
  cout << x << "\n";
  return 0;
}
