import java.util.Arrays;
import java.util.Scanner;

public class Yukicoder67 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] l = new int[n];
		int sum = 0;
		for (int i = 0; i < n; i++) {
			l[i] = sc.nextInt();
			sum += l[i];
		}
		int k = sc.nextInt();
		Arrays.sort(l);
		
		double low = 0, high = (double) sum / (double) k, mid = 0;
		for (int i = 0; i < 100; i++) {
			long count = 0;
			mid = (high + low) / 2.0;
//			System.out.println("mid = " + mid);
			if (isEnable(l, 0, k, mid)) {
				low = mid;
			} else {
				high = mid;
			}

		}
		System.out.println(mid);
	}
	static boolean isEnable(int[] l, int index, int k, double mid){
		if (index == l.length) {
			return false;
		}
		for (int i = k; i > 0; i--) {
			if ((double) l[l.length - index - 1] / (double) i >= mid) {
				if (i == k)
					return true;
				else 
					return isEnable(l, index+1, k-i, mid);
			}
		}
		return false;
	}
}