import java.util.*;
import java.io.*;
import java.awt.geom.*;
import java.math.*;

public class No0067 {

	static final Scanner in = new Scanner(System.in);
	static final PrintWriter out = new PrintWriter(System.out,false);

	static void solve() {
		int n = in.nextInt();
		int[] l = new int[n];
		int max = 0;
		for (int i=0; i<n; i++) {
			l[i] = in.nextInt();
			max = Math.max(max, l[i]);
		}
		long k = in.nextLong();

		double lb = 0, ub = max;
		for (int i=0; i<100; i++) {
			double m = (lb + ub)/2;
			if (cnt(l,m) >= k) lb = m;
			else ub = m;
		}

		out.printf("%.10f\n",ub);
	}

	static long cnt(int[] l, double m) {
		long res = 0;
		for (int i=0; i<l.length; i++) {
			res += (long)(l[i]/m);
		}
		return res;
	}

	public static void main(String[] args) {
		long start = System.currentTimeMillis();

		solve();
		out.flush();

		long end = System.currentTimeMillis();
		//trace(end-start + "ms");
		in.close();
		out.close();
	}

	static void trace(Object... o) { System.out.println(Arrays.deepToString(o));}
}