#include <iostream>
#include <iomanip>
#include <algorithm>
#include <vector>
#include <string>
#include <queue>
#include <stack>
#include <functional>
#include <complex>
#include <cmath>
#include <ccomplex>

using namespace std;

int main() {
	int n;
	cin >> n;
	vector<int> v(n);
	for (int i = 0; i < n; i++)cin >> v[i];
	long long k;
	cin >> k;
	
	sort(v.begin(), v.end(), greater<int>());

	const double eps = 1e-9;
	double high = v[0];
	double low = 0;
	
	while (high - low > eps && (high - low) / high > eps){
		double mid = (high + low) / 2;
		
		long long cnt = 0;
		for (int i = 0; i < n; i++) {
			cnt += v[i] / mid;
		}

		cerr << high << " " << mid << " " << low << " " << cnt << endl;
		if (cnt >= k) {
			low = mid;
		}
		else {
			high = mid;
		}
	}
	cout << fixed << setprecision(20) << high << endl;

}