#include <bits/stdc++.h>
using namespace std;
int main() {
  cin.tie(0);
  cin.sync_with_stdio(0);
  cout.tie(0);
  int n, k;
  double a[5001], s[5001], somma = 0.0, massimo = -1e9;
  cin >> n >> k;
  for (int i = 0; i < n; i++) cin >> a[i];
  for (int j = k; j <= min(n, 2 * k); j++) {
    for (int i = 0; i < n; i++) s[i] = 0.0;
    for (int i = 0; i < j; i++) s[0] += a[i];
    massimo = max(massimo, s[0] / (double)j);
    for (int i = 1; i < n - j + 1; i++) {
      s[i] = s[i - 1] + a[i + j - 1] - a[i - 1];
      massimo = max(massimo, s[i] / (double)j);
    }
  }
  cout << setprecision(14) << massimo;
  return 0;
}
