#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10;
int a[N];
int main() {
  int n, k;
  scanf("%d%d", &n, &k);
  double ans = 0;
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  for (int i = 1; i <= n; i++) {
    double sum = 0;
    for (int j = i; j <= n; j++) {
      sum += a[j];
      if (j - i + 1 >= k) ans = max(ans, sum / (j - i + 1));
    }
  }
  printf("%.15f\n", ans);
  return 0;
}
