#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  int a[50000] = {0}, i, j;
  double ans = 0;
  for (i = 1; i <= n; i++) cin >> a[i], a[i] += a[i - 1];
  for (i = 0; i <= n; i++) {
    for (j = i + k; j <= n; j++) {
      ans = max(ans, (1.0 * abs(a[j] - a[i])) / (1.0 * (j - i)));
    }
  }
  cout << setprecision(15) << ans << endl;
}
