#include <bits/stdc++.h>
using namespace std;
const double EPS = 1e-6;
const int MOD = 1e9 + 7;
int a[5000], pref[5001];
int main() {
  int n, k;
  scanf("%d%d", &n, &k);
  pref[0] = 0;
  for (int i = 0; i < n; i++) {
    scanf("%d", &a[i]);
    pref[i + 1] = pref[i] + a[i];
  }
  double mx = 0;
  for (int i = 0; i < n; i++) {
    for (int j = k - 1; j < n - i; j++) {
      mx = max(mx, double(pref[i + j + 1] - pref[i]) / (j + 1));
    }
  }
  printf("%0.7lf", mx);
  return 0;
}
