#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
#define rep(i, n) REP(i, 0, n)
#define REP(i, s, e) for (ll i = (s); i < (ll)(e); i++)
#define repr(i, n) REPR(i, n, 0)
#define REPR(i, s, e) for (ll i = (ll)(s - 1); i >= (ll)(e); i--)
#define all(r) r.begin(), r.end()
#define rall(r) r.rbegin(), r.rend()

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;

template <typename T, typename U>
bool chmax(T& a, const U& b) {
    if (a >= b) return false;
    a = b;
    return true;
}
template <typename T, typename U>
bool chmin(T& a, const U& b) {
    if (a <= b) return false;
    a = b;
    return true;
}

void yes_no(bool f, string yes = "Yes", string no = "No") {
    cout << (f ? yes : no) << "\n";
}

void solve() {
    int n;
    cin >> n;
    using D = long double;
    vector<D> a(n);
    rep(i, n) cin >> a[i];
    ll k;
    cin >> k;
    auto jd = [&](D mid) {
        ll sum = 0;
        rep(i, n) {
            sum += a[i] / mid;
            if (sum >= k) return true;
        }
        return false;
    };
    D ok = 0, ng = 1e18;
    rep(_, 256) {
        D mid = (ok + ng) / 2;
        if (jd(mid)) ok = mid;
        else ng = mid;
    }
    cout << fixed << setprecision(15);
    cout << ok << "\n";
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int t = 1;
    // cin >> t;
    rep(ti, t) solve();
    return 0;
}