#include <bits/stdc++.h>
using namespace std;
const int MAX = 5005;
int a[MAX];
long long pref[MAX];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  int n, k;
  cin >> n >> k;
  pref[0] = 0;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    pref[i] = pref[i - 1] + a[i];
  }
  long double ans = -1e18;
  for (int i = k; i <= n; i++)
    for (int l = 0, r = i; r != n + 1; l++, r++)
      ans = max(ans, (long double)(pref[r] - pref[l]) / i);
  cout << fixed << setprecision(10) << ans << endl;
  return 0;
}
