#include <bits/stdc++.h>

using namespace std;

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n;
  cin >> n;

  vector<double> l(n);
  for (int i = 0; i < n; i++)
    cin >> l[i];

  long long k;
  cin >> k;

  double lo = 0, hi = 1e9;
  for (int t = 0; t < 100; t++) {
    double mi = (lo + hi) / 2;
    long long cnt = 0;
    for (double x : l)
      cnt += x / mi;
    
    if (cnt >= k)
      lo = mi;
    else
      hi = mi;
  }
  
  cout << fixed << setprecision(12) << lo << endl;

  return 0;
}