#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int n;
vector<int>v;
int k;
bool ok(double mid) {
	ll ans = 0;
	for (int i = 0; i < n; i++) {
		ans += (v[i] / mid);
	}
	return (ans >= k);
}
int main() {
// #ifndef ONLINE_JUDGE
// 	freopen("input.txt", "r", stdin);
// 	freopen("output.txt", "w", stdout);
// #endif
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cin >> n;
	v.resize(n);
	for (int i = 0; i < n; i++) {
		cin >> v[i];
	}
	cin >> k;
	double long left = 0, right = 1e9 + 1;
	for (int rep = 0; rep < 80; rep++) {
		double long mid = (left + right) / 2.0;
		if (ok(mid))left = mid;
		else right = mid;
	}
	cout << setprecision(9) << fixed << left << endl;
}