#include <bits/stdc++.h>
using namespace std;
const long double PI = 3.1415926535897932384626433832795;
template <typename T>
T max3(T n1, T n2, T n3) {
  return max(n1, max(n2, n3));
}
template <typename T>
T min3(T n1, T n2, T n3) {
  return max(n1, max(n2, n3));
}
int main() {
  int n, k;
  cin >> n >> k;
  long long arr[n];
  for (int i = 0; i < n; i++) cin >> arr[i];
  long double sum = 0;
  long double maxi = 0;
  for (int i = 0; i < n; i++) {
    sum = arr[i];
    if (k == 1) maxi = max(maxi, sum);
    for (int j = i + 1; j < n; j++) {
      sum += arr[j];
      if (j - i + 1 >= k) maxi = max(maxi, sum / (j - i + 1));
    }
  }
  cout << setprecision(6) << fixed << maxi << endl;
}
