#include <iostream>
#include <algorithm>
#include <vector>
#include <iomanip>
using namespace std;

typedef long long ll;
typedef pair<int, int> P;
const int INF = (int)1e9 + 1;

ll n, l[20010], k;

int main(void) {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> l[i];
	}
	cin >> k;

	double low = 0.0;
	double high = 1e9;

	for (int t = 0; t < 100; t++) {
		double mid = (low + high) / 2;
		ll temp = 0;
		for (int i = 0; i < n; i++) {
			temp += (ll)(l[i] / mid);
		}

		if (temp >= k) low = mid;
		else high = mid;
	}
	cout << fixed << setprecision(10) << low << endl;
	return 0;
}