#include <bits/stdc++.h>
using namespace std;
const int N = 5005;
int a[N], sum[N];
int main() {
  int n, k;
  scanf("%d%d", &n, &k);
  for (int i = 1; i <= n; i++) {
    scanf("%d", a + i);
    sum[i] = sum[i - 1] + a[i];
  }
  double res = -1e30;
  for (int i = 1; i <= n; i++) {
    for (int j = i + k - 1; j <= n; j++) {
      res = max(res, double(sum[j] - sum[i - 1]) / (j - i + 1));
    }
  }
  printf("%.15f\n", res);
}
