#include <bits/stdc++.h>
using namespace std;
int n, k, a[10000];
int main() {
  scanf("%d%d", &n, &k);
  for (int i = 1; i <= n; ++i) scanf("%d", &a[i]), a[i] += a[i - 1];
  double ans = 0;
  for (int i = 0; i <= n; ++i)
    for (int j = i + k; j <= n; ++j)
      ans = max(ans, 1. * (a[j] - a[i]) / (j - i));
  printf("%.10lf", ans);
}
