#include <bits/stdc++.h>
using namespace std;
long long mod = 1e9 + 7;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long t;
  double k;
  cin >> t >> k;
  vector<double> v(t);
  for (long long i = 0; i < t; i++) cin >> v[i];
  long long s = 0, ans;
  double out = INT_MIN;
  while (k <= t) {
    s = 0;
    for (long long i = 0; i < k; i++) s += v[i];
    ans = s;
    for (int i = k; i < t; i++) {
      s += v[i] - v[i - k];
      ans = max(ans, s);
    }
    double temp = (double)ans / k;
    if (out < temp) out = temp;
    k++;
  }
  cout << setprecision(10) << out << '\n';
  return 0;
}
