#include <bits/stdc++.h>
using namespace std;
double a[10005], sum[10005];
int main() {
  int n, k;
  cin >> n >> k;
  sum[0] = 0;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    sum[i] = sum[i - 1] + a[i];
  }
  double maxa = 0;
  for (int i = 0; i <= n - k; i++) {
    for (int j = 0; i + j <= n - k; j++) {
      maxa = max(maxa, (sum[i + k + j] - sum[i]) / (j + k));
    }
  }
  cout << fixed << setprecision(10) << maxa << '\n';
}
