#include "bits/stdc++.h"
#define all(x) (x).begin(), (x).end()
#define rep(i,from,to) for (int (i) = (from); (i) < (to); ++(i))
#define repi(x) for (int i = 0; i < (x); ++i)
#define repj(x) for (int j = 0; j < (x); ++j)
using namespace std;
typedef long long ll;
const ll INF = 1LL << 60;
const ll MOD = 1e9 + 7;

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


int main() {
	ll N;
	cin >> N;
	vector<double> L(N);
	repi(N) cin >> L[i];
	ll K;
	cin >> K;

	double l = 0, r = 1e10;
	double mid = 0;
	rep(i,0,100) {
		mid = (r + l) / 2;
		ll a = 0;
		for (int j = 0; j < N; ++j) {
			a += L[j] / mid;
		}
		if (a >= K) l = mid;
		else r = mid;
	}
	cout << fixed << setprecision(10) << mid << endl;
	return 0;
}