#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k;
  cin >> n >> k;
  int a[5005];
  a[0] = 0;
  for (int i = 1; i <= n; ++i) cin >> a[i];
  for (int i = 1; i <= n; ++i) a[i] = a[i] + a[i - 1];
  double ans = 0;
  int sum;
  for (int j = k; j <= n; ++j)
    for (int i = j; i <= n; ++i) ans = max(ans, (double)(a[i] - a[i - j]) / j);
  printf("%.15lf", ans);
  return 0;
}
