#include <algorithm>
#include <iostream>
#include <vector>
#include <cassert>
using namespace std;
using ll = long long;

vector<int> ls;
ll k;

bool check(double x) {
    ll cnt = 0;
    for (int l: ls) cnt += l / x;
    return cnt >= k;
}

double binary_search(double ok, double ng) {
    assert(check(ok) == true);
    assert(check(ng) == false);
    for (int i = 0; i < 100; i++) {
        double mid = (ng + ok) / 2;
        (check(mid) ? ok : ng) = mid;
    }
    return ok;
}

#include <iomanip>
int main() {
    cout << fixed << setprecision(12);
    int n; cin >> n;
    ls.resize(n);
    for (int &l: ls) cin >> l;
    cin >> k;
    double ok = n / k;
    double ng = 1e12;
    cout << binary_search(ok, ng) << endl;
    return 0;
}