#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k;
  cin >> n >> k;
  double a[n];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  double resp = 0;
  for (int i = 0; i < n; i++) {
    double tSum = 0;
    for (int j = i; j < n; j++) {
      tSum += a[j];
      double aux = tSum / (j - i + 1);
      if (aux > resp && (j - i + 1) >= k) {
        resp = aux;
      }
    }
  }
  cout << setprecision(15);
  cout << resp;
  return 0;
}
