#include <bits/stdc++.h>
using namespace std;
double a[5050], sum[5050];
int main() {
  int n, k, i, j;
  double maxx = 0;
  cin >> n >> k;
  for (i = 1; i <= n; i++) cin >> a[i];
  sum[1] = a[1];
  for (i = 2; i <= n; i++) sum[i] = sum[i - 1] + a[i];
  for (i = 1; i <= n; i++) {
    for (j = i; j <= n; j++) {
      if (j - i + 1 >= k) {
        double t = (sum[j] - sum[i - 1]) / (double)(j - i + 1.0);
        maxx = max(maxx, t);
      }
    }
  }
  printf("%lf\n", maxx);
  return 0;
}
