#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 ==================================

// template <typename T, typename Predicate>
// T bisection(T false_side, T true_side, Predicate pred, T tolerant = 1) {
//     assert(!is_integral_v<T> || tolerant == 1);
//     while ((false_side > true_side ? false_side - true_side : true_side - false_side) > tolerant) {
//         T mid_value = is_integral_v<T>
//             ? false_side / 2 + true_side / 2 + ("AABBC"[2 + false_side % 2 + true_side % 2] - 'B')
//             : (false_side + true_side) * 0.5;
//         (pred(mid_value) ? true_side : false_side) = mid_value;
//     }
//     return true_side;
// }
template <typename Predicate>
double bisection(double false_side, double true_side, Predicate pred, double tolerant = 1) {
    // assert(!is_integral_v<double> || tolerant == 1);
    while ((false_side > true_side ? false_side - true_side : true_side - false_side) > tolerant) {
        double mid_value = (false_side + true_side) * 0.5;
        (pred(mid_value) ? true_side : false_side) = mid_value;
    }
    return true_side;
}

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