#include <bits/stdc++.h>
using namespace std;
const double INF = 2000000000;
int main(){
  cout << fixed << setprecision(20);
  int N;
  cin >> N;
  vector<int> L(N);
  for (int i = 0; i < N; i++){
    cin >> L[i];
  }
  long long K;
  cin >> K;
  double tv = 0;
  double fv = INF;
  for (int i = 0; i < 100; i++){
    double mid = (tv + fv) / 2;
    long long sum = 0;
    for (int j = 0; j < N; j++){
      sum += L[j] / mid;
    }
    if (sum >= K){
      tv = mid;
    } else {
      fv = mid;
    }
  }
  cout << tv << endl;
}