#include <bits/stdc++.h>
using namespace std;
double ans;
int n, k;
double a[5005], sum[5005];
int main() {
  ans = 0;
  scanf("%d%d", &n, &k);
  for (int(i) = (1); (i) <= (n); (i)++) {
    scanf("%lf", &a[i]);
    sum[i] = sum[i - 1] + a[i];
  }
  for (int(i) = (1); (i) <= (n); (i)++)
    for (int(j) = (i + k - 1); (j) <= (n); (j)++) {
      double temp = sum[j] - sum[i - 1];
      if (temp / (double)(j - i + 1) > ans) ans = temp / (double)(j - i + 1);
    }
  printf("%.7f", ans);
}
