#include <bits/stdc++.h>

using namespace std;

namespace {

    typedef double real;
    typedef long long ll;

    template<class T> ostream& operator<<(ostream& os, const vector<T>& vs) {
        if (vs.empty()) return os << "[]";
        os << "[" << vs[0];
        for (int i = 1; i < vs.size(); i++) os << " " << vs[i];
        return os << "]";
    }
    template<class T> istream& operator>>(istream& is, vector<T>& vs) {
        for (auto it = vs.begin(); it != vs.end(); it++) is >> *it;
        return is;
    }

    int N;
    vector<real> L;
    ll K;
    void input() {
        cin >> N;
        L.resize(N); cin >> L;
        cin >> K;
    }

    bool check(real x) {
        ll count = 0;
        for (int i = 0; i < N; i++) {
            count += ll(L[i] / x);
        }
        return count >= K;
    }

    void solve() {
        real lb = 0, ub = 1e9 + 5;
        for (int i = 0; i < 100; i++) {
            real mid = (lb + ub) / 2;
            if (check(mid)) {
                lb = mid;
            } else {
                ub = mid;
            }
        }
        cout << setprecision(15) << lb << endl;
    }
}

int main() {
    input(); solve();
    return 0;
}