#include <iostream>
#include <vector>
#include <stdio.h>
using namespace std;
int main(){
    int n;
    cin >> n;
    vector<long long> l(n);
    for(auto& i: l) cin >> i;
    long long k;
    cin >> k;
    double d = 0, u = 1e9, m;
    for(int i=0; i<100; ++i){
        m = (d+u)/2;
        long long s = 0;
        for(auto j: l) s += j/m;
        if(s < k) u = m;
        else d = m;
    }
    printf("%.9f\n", m);
    return 0;
}