import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    double[] l = new double[n];
    for(int i = 0; i < n; i++) {
      l[i] = sc.nextDouble();
    }
    long k = sc.nextLong();
    double ans = 0;
    double left = 0;
    double right = 1000000001;
    for(int i = 0; i < 70; i++) {
      double med = (left + right) / 2;
      long t = 0;
      for(int j = 0; j < n; j++) {
        t += ((long)(l[j] / med));
      }
      if(t >= k) {
        ans = med;
        left = med;
      } else {
        right = med;
      }
    }
    System.out.println(ans);
  }
}