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

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int[] values = new int[n];
        for (int i = 0; i < n; i++) {
            values[i] = sc.nextInt();
        }
        long k = sc.nextLong();
        double left = 1.0 / k;
        double right = Integer.MAX_VALUE;
        for (int i = 0; i < 1000; i++) {
            long sum = 0;
            double m = (left + right) / 2;
            for (int j = 0; j < n && sum < k; j++) {
                sum += (long)(values[j] / m);
            }
            if (sum >= k) {
                left = m;
            } else {
                right = m;
            }
        }
        System.out.println(new java.math.BigDecimal(left).toPlainString());
    }
    
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String nextLine() throws Exception {
        return br.readLine();
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}