#include <iostream>
#include <vector>
#include <iomanip>
using namespace std;

vector<int> L;
int k;

bool check(double x){
    long long s = 0;
    for(int i = 0; i < (int)L.size(); i++) s += L[i] / x;
    if(s >= k) return true;
    else return false;
}

int main(){
    int n;
    cin >> n;

    L.assign(n, 0);
    for(int i = 0; i < n; i++) cin >> L[i];
    cin >> k;

    double l = 0, r = 1e18;

    /*
    while(r - l > 0.0000000001){
        double mid = (l + r) / 2;
        if(check(mid)) l = mid;
        else r = mid;
    }*/

    for(int i = 0; i < 100; i++){
        double mid = (l + r) / 2;
        if(check(mid)) l = mid;
        else r = mid;
    }

    //cout << l << " " << r << endl;
    cout << setprecision(20) << l << endl;
    
}