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


public class Main_yukicoder67 {

    public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		Printer pr = new Printer(System.out);

		int n = sc.nextInt();

		int[] l = new int[n];
		for (int i = 0; i < n; i++) {
			l[i] = sc.nextInt();
		}

		long k = sc.nextLong();

		double ll = 0;
		double rr = 1_000_000_000;
		for (int i = 0; i < 100; i++) {
			double mid = ll + (rr - ll) / 2;

			if (isOK(mid, l, k)) {
				ll = mid;
			} else {
				rr = mid;
			}
		}

		pr.printf("%.10f\n", rr);

		pr.close();
		sc.close();
    }

	private static boolean isOK(double mid, int[] l, long k) {
		long cnt = 0;
		for (int e : l) {
			cnt += (long)(e / mid);
		}

		return cnt >= k;
	}

	@SuppressWarnings("unused")
	private static class Scanner {
		BufferedReader br;
		Iterator<String> it;

		Scanner (InputStream in) {
			br = new BufferedReader(new InputStreamReader(in));
		}

		String next() throws RuntimeException  {
			try {
				if (it == null || !it.hasNext()) {
					it = Arrays.asList(br.readLine().split(" ")).iterator();
				}
				return it.next();
			} catch (IOException e) {
				throw new IllegalStateException();
			}
		}

		int nextInt() throws RuntimeException {
			return Integer.parseInt(next());
		}

		long nextLong() throws RuntimeException {
			return Long.parseLong(next());
		}

		float nextFloat() throws RuntimeException {
			return Float.parseFloat(next());
		}

		double nextDouble() throws RuntimeException {
			return Double.parseDouble(next());
		}

		void close() {
			try {
				br.close();
			} catch (IOException e) {
//				throw new IllegalStateException();
			}
		}
	}

	private static class Printer extends PrintWriter {
		Printer(PrintStream out) {
			super(out);
		}
	}
}