#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <queue>
#include <complex>

#define INF_MIN 100000000
#define INF 1145141919
#define INF_MAX 2147483647
#define LL_MAX 9223372036854775807
#define EPS 1e-10
#define PI acos(-1)
#define LL long long

using namespace std;

#define MAX_N 200001
int N;
double L[MAX_N];
LL K;

bool check(double mid){

  LL ret = 0;
  
  for(int i = 0; i < N; i++){
    ret += (int)(L[i] / mid);
  }

  if(ret >= K)
    return true;
  else
    return false;

}

int main(){

  cin >> N;
  for(int i = 0; i < N; i++){
    cin >> L[i];
  }
  cin >> K;

  double ansL = 0.0, ansR = (1e+9) + 1.0;

  for(int i = 0; i < 100; i++){
    
    double mid = (ansR + ansL)/2.0;

    if(check(mid)){
      ansL = mid;
    }
    else{
      ansR = mid;
    }

  }

  printf("%.15f\n", ansL);

  return 0;

}