import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        float[] l = new float[n];
        float max = 0;
        for (int i = 0; i < n; i++) {
            l[i] = sc.nextFloat();
            max = Math.max(max, l[i]);
        }
        long k = sc.nextLong();
        float ans = binSearch(0, max + 1, k, l, n);
        // System.out.println(Arrays.toString(l));
        // System.out.println(ans);
        System.out.printf("%.9f%n", ans);
    }
    public static float binSearch(float ok, float ng, long k, float[] l, int n) {
        for (int i = 0; i < 100; i++) {
            float mid = (ok + ng) / (float) 2;
            // System.out.printf("ok = %f%n", ok);
            // System.out.printf("ng = %f%n", ng);
            // System.out.printf("mid = %f%n", mid);
            if (solve(mid, k, l, n)) {
                ok = mid;
            } else {
                ng = mid;
            }
        }
        return ok;
    }
    public static boolean solve(float x, long k, float[] l, int n) {
        long cnt = 0;
        for (int i = 0; i < n; i++) {
            cnt += l[i] / x;
        }
        if (cnt < k) {
            return false;
        }
        return true;
    }
}