#include <bits/stdc++.h>
using namespace std;
long double maxm(long double a, long double b) {
  if (a > b)
    return a;
  else
    return b;
}
int main() {
  int n, k;
  cin >> n >> k;
  int a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  long double answer = 0;
  while (k <= n) {
    long double average = 0;
    int sum = 0;
    for (int i = 0; i < k; i++) {
      sum += a[i];
    }
    average = (long double)sum / k;
    long double t;
    for (int i = k; i < n; i++) {
      sum = sum - a[i - k];
      sum = sum + a[i];
      t = (long double)sum / k;
      average = maxm(average, t);
    }
    answer = maxm(answer, average);
    k++;
  }
  cout << setprecision(20) << answer << endl;
}
