#include <bits/stdc++.h>
using namespace std;
int n, k, prefix[5005];
int main() {
  cin >> n >> k;
  for (int i = 0; i < n; i++) {
    int t;
    cin >> t;
    prefix[i + 1] = prefix[i] + t;
  }
  long double m = -1234567890;
  for (int i = 0; i < n - k + 1; i++) {
    for (int j = i + k - 1; j < n; j++) {
      m = max(m, (long double)(prefix[j + 1] - prefix[i]) / (j - i + 1));
    }
  }
  cout << fixed << setprecision(10) << m << '\n';
  return 0;
}
