#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = (int)1e9 + 1001010;
const ll llINF = (ll)4e18 + 11000010;
#define ALL(x) x.begin(),x.end()
#define RALL(x) x.rbegin(),x.rend()
ll ceil(ll a, ll b){return (a+b-1) / b;};
// ================================== ここまでテンプレ ==================================

// とある条件を満たす区間の境界を見つける
// 探索区間は [ok, ng) または (ng, ok]
// ok はつねに「とある条件」を満たす
// ng はつねに「とある条件」を満たさない
// 「とある条件」を満たすかどうかは、judge関数によって求められる
template<class T, class Judgement>
T Binary_Search(T ok, T ng, Judgement judge, T tolerance = 1){
    assert(!is_integral_v<T> || tolerance == 1);
    while(((ok < ng) ? (ng - ok) : (ok - ng)) > tolerance){
    // while(abs(ok - ng) > 1) {
        T mid;
        if(is_integral_v<T>){
            if(ok > 0 ^ ng > 0) mid = ok + (ng - ok)/2;
            else mid = (ok + ng)/2;
        }
        else mid = (ok + ng) * 0.5;

        if(judge(mid)) ok = mid;
        else ng = mid;
    }
    return ok;
};

int main(){
    int n; cin >> n;
    vector<double> l(n);
    for(int i = 0; i < n; i++) cin >> l[i];
    ll k; cin >> k;

    auto judge = [&](double mid) -> bool{
        if(mid <= 0) return true;
        int count = 0;
        for(int i = 0; i < n; i++){
            count += floor(l[i] / mid);
        }
        return (count >= k);
    };

    double ans = Binary_Search(-1.0, 1e12, judge, 1e-10);
    printf("%.12lf\n", ans);
    return 0;
}