#include <bits/stdc++.h>
using namespace std;
int n, k;
double a[5001], pref[5001];
int main() {
  cin >> n >> k;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    pref[i] += pref[i - 1] + a[i];
  }
  double ans = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = i; j <= n; j++) {
      if (j - i + 1 >= k) {
        double kol = j - i + 1;
        double ans2 = (pref[j] - pref[i - 1]) / kol;
        ans = max(ans, ans2);
      }
    }
  }
  cout << fixed << setprecision(9) << ans;
}
