#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k;
  cin >> n >> k;
  int arr[n];
  int su[n];
  int sum = 0;
  long double ans = 0;
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
    sum += arr[i];
    su[i] = sum;
  }
  for (int i = 0; i <= n - k; i++) {
    for (int j = i + k - 1; j < n; j++) {
      ans = max(ans, (long double)(su[j] - su[i] + arr[i]) /
                         (long double)(j - i + 1));
    }
  }
  cout << setprecision(10);
  cout << ans << "\n";
}
