#include <bits/stdc++.h>
using namespace std;
long double a[5005];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
    a[i] += a[i - 1];
  }
  long double ans = -1e9;
  for (int i = 1; i <= n; ++i) {
    for (int j = i + k - 1; j <= n; ++j) {
      long double temp = (double)(a[j] - a[i - 1]) / (double)(j - i + 1);
      if (ans < temp) ans = temp;
    }
  }
  cout << fixed << setprecision(12) << ans;
}
