#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>

int N;
std::vector<long long int> L;
long K;

long long int separate(double length){
    long long int num = 0;
    for(int i=0; i<N; ++i){
        num += L[i]/length;
    }
    return num;
}

int main(void){
    std::cin >> N;
    L.resize(N);
    for(int i=0; i<N; ++i) std::cin >> L[i];
    std::cin >> K;

    double left  = .0;
    double right = 1e11;
    double mid;

    for(int i=0; i<100; ++i){
        mid = (left+right)*.5;

        if(separate(mid) >= K){
            left = mid;
        }else{
            right = mid;
        }
    }
    std::cout << std::fixed << std::setprecision(9) << left << std::endl;
}