#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  int n, k, i, j;
  cin >> n >> k;
  double max = 0.00000, t = 0.00000;
  int a[n], cf[n + 1];
  cf[0] = 0;
  for (i = 0; i < n; i++) {
    cin >> a[i];
    cf[i + 1] = a[i] + cf[i];
  }
  for (j = k; j <= n; j++) {
    for (i = 0; i <= n - j; i++) {
      t = (double)(cf[i + j] - cf[i]) / j;
      if (t > max) max = t;
    }
  }
  cout << fixed << setprecision(16) << max;
  return 0;
}
