import java.util.*;
import java.io.*;

public class Main{
	static int N;
	static int[] l;
	static int K;
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		N = sc.nextInt();
		l = new int[N];
		for(int i=0; i<N; i++){
			l[i] = sc.nextInt();
		}
		K = sc.nextInt();

		double lb = 0, ub = 1e12;
		for(int cnt = 0; cnt < 100; cnt++) { // while (ub - lb > 1)
			double mid = (lb + ub) / 2;

			if (mid < 1e-10) {
				lb = mid;
				continue;
			}

			int sum = 0;
			for(int i=0; i<N; i++){
				sum += l[i] / mid;
			}

			if (sum >= K) lb = mid;
			else ub = mid;
		}

		System.out.println(lb);
	}
}