#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n, k;
  cin >> n >> k;
  int ar[n + 5];
  for (int i = 0; i < n; i++) {
    cin >> ar[i];
  }
  double maxm = 0.00;
  for (int i = 0; i < n; i++) {
    double sum = 0;
    double cnt = 0;
    for (int j = i; j < n; j++) {
      sum = sum + ar[j];
      cnt = cnt + 1;
      if (cnt >= k) {
        double avg = (double)sum / (double)cnt;
        maxm = max(maxm, avg);
      }
    }
  }
  cout << fixed << setprecision(15) << maxm << endl;
  return 0;
}
