#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

const double EPS = 1e-9;

using namespace std;

int main() {
	int n;
	long long k;

	cin >> n;
	vector<double> l(n, 0);
	for (int i = 0; i < n; i++) {
		cin >> l[i];
	}
	cin >> k;

	double upper = 1e9;
	double lower = 0;
	double mid;

	long long count;
	while (upper - lower > EPS && upper > lower * (EPS + 1)) {
		mid = (upper + lower) / 2;
		count = 0;
		for (int i = 0; i < n; i++) {
			count += l[i] / mid;
		}

		if (count >= k) {
			lower = mid;
		} else {
			upper = mid;
		}
	}

	printf("%.10f\n", mid);
	return 0;
}