/* -*- coding: utf-8 -*-
 *
 * 67.cc: No.67 よくある棒を切る問題 (1) - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 200000;

/* typedef */

typedef long long ll;

/* global variables */

int n;
double ls[MAX_N];
ll k;

/* subroutines */

ll cut(double l) {
  ll sum = 0;
  for (int i = 0; i < n; i++) sum += (ll)(ls[i] / l);
  return sum;
}

/* main */

int main() {
  cin >> n;
  for (int i = 0; i < n; i++) cin >> ls[i];
  cin >> k;

  double l0 = 0.0, l1 = 1e9;
  for (int i = 0; i < 100; i++) {
    double l = (l0 + l1) / 2;
    if (cut(l) < k) l1 = l;
    else l0 = l;
  }

  printf("%.14lf\n", l1);
  return 0;
}