#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int k;
  cin >> k;
  double res = 0;
  vector<double> v(n);
  for (int i = 0; i < n; ++i) cin >> v[i];
  for (int i = 0; i < n; ++i) {
    double s = 0;
    for (int j = i; j < n; ++j) {
      s += v[j];
      if (j - i + 1 >= k) res = max(res, s / (j - i + 1));
    }
  }
  printf("%.9lf\n", res);
  return 0;
}
