#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int k, n;
  cin >> n >> k;
  int x[n];
  for (int i = 0; i < n; i++) {
    cin >> x[i];
  }
  double m = -1, sum = 0;
  int c = 0;
  for (int i = 0; i < n; i++) {
    for (int j = i; j < n; j++) {
      c++;
      sum += x[j];
      if (c >= k && (sum / c) > m) {
        m = sum / c;
      }
    }
    c = 0;
    sum = 0;
  }
  cout << setprecision(15) << fixed << m << endl;
}
