#include <bits/stdc++.h>
// #include <boost/multiprecision/cpp_int.hpp>
using namespace std;
// using bigint = boost::multiprecision::cpp_int;

template <typename T> using min_priority_queue = priority_queue<T,vector<T>,greater<T>>;

random_device seed_gen;
mt19937 engine(seed_gen());

int64_t get_time_ns(){
    struct::timespec t;
    clock_gettime(CLOCK_MONOTONIC, &t);
    return t.tv_sec * int64_t(1'000'000'000) + t.tv_nsec;
}

int main() {
    int n; cin >> n;
    vector<int64_t> L(n);
    for(int64_t &l : L) cin >> l;
    int64_t k; cin >> k;

    double ok = 1e-10;
    double ng = 1e15;
    while((ng - ok) / ok > 1e-9) {
        double mid = sqrt(ok * ng);
        int64_t cnt = 0;
        for(int64_t l : L) cnt += floor(l / mid);
        if(cnt >= k) ok = mid;
        else ng = mid;
    }

    cout << fixed << setprecision(20) << ok << endl;
    return 0;
}