#include <bits/stdc++.h>
using namespace std;
double arr[10002], num[10002];
int main() {
  long long n, m;
  cin >> n >> m;
  for (long long i = 1; i <= n; i++) {
    cin >> arr[i];
    arr[i] = arr[i] + arr[i - 1];
  }
  double mx = 0;
  for (long long i = 1; i <= n; i++) {
    for (long long j = i + m - 1; j <= n; j++) {
      mx = max(mx, (arr[j] - arr[i - 1]) / (j - i + 1));
    }
  }
  cout << setprecision(15) << fixed << mx << endl;
}
