#include <iostream>
#include <iomanip>

typedef long long int Int;
const Int MAX_INT = 1000000000;
const double EPS = 1e-9;

Int min(Int L[], Int N) {
	Int min_val = MAX_INT;
	for (Int i=0; i<N; i++) {
		if (min_val > L[i]) min_val = L[i];
	}
	return min_val;
}

Int sum(Int L[], Int N) {
	Int sum_val = 0;
	for (Int i=0; i<N; i++) sum_val += L[i];
	return sum_val;
}

bool retrievable(double x, Int L[], Int N, Int K) {
	Int max_num = 0;
	for (Int i=0; i<N; i++) {
		max_num += (Int)(L[i] / x);
	}
	return max_num >= K;
}

double find(double a, double b, Int L[], Int N, Int K) {
	if ((b - a) / a < EPS) {
		return a;
	} else {
		double c = (a + b) / 2;
		if (retrievable(c, L, N, K)) {
			return find(c, b, L, N, K);
		} else {
			return find(a, c, L, N, K);
		}
	}
}

int main() {
	Int N;
	std::cin >> N;
	Int L[N];
	for (Int i=0; i<N; i++)
		std::cin >> L[i];
	Int K;
	std::cin >> K;
	
	double a = (double)min(L, N) / (double)K;
	double b = (double)sum(L, N) / (K-0.1) ;
	
	std::cout << std::setprecision(9)
			<< find(a, b, L, N, K) << std::endl;
	
	return 0;
}