import java.util.Scanner;

public class N067
{
	static double max=0,min=Math.pow(10, -9),ans,k;
	static int n;
	static int[] l;
	public static void main(String[] args)
	{
		Scanner sc = new Scanner(System.in);
		n=sc.nextInt();

		l=new int[n];
		max=0;min=0;

		for(int i=0;i<n;i++)
		{
			l[i]=sc.nextInt();
			max=(l[i]>max)?l[i]:max;
		}
		k=sc.nextInt();

		if(isok(max))
		{
			System.out.println(max);
		}
		else
		{
			nibun(min,max);
			System.out.printf("%.8f",ans);
		}


	}

	static void nibun(double min,double max)
	{
		double av=(max+min)/2;
		double dif=max-min;
		if(dif<Math.pow(10, -8))
		{
			ans=av;
			return;
		}
		else
		{
			if(isok(av))
			{
				nibun(av,max);
			}
			else
			{
				nibun(min,av);
			}
		}
	}

	static boolean isok(double a)
	{
		int cnt=0;
		int end=0;
		for(int i=0;end==0&&i<n;i++)
		{
			cnt+=(int)(l[i]/a);
			if(cnt>=k)
			{end=1;}
		}
		if(end==1)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
}