using System;
using System.Collections;
using System.Collections.Generic;
 
class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	public void Solve(){
		
		Array.Sort(L,(x,y)=>x>y?-1:x<y?1:0);
		
		double r=(2e10);
		double l=0.0;
		double c=0.0;
		int times=200;
		long cnt=0;
		for(;times>0;times--){
			c=(l+r)/2;
			cnt=0;
			for(int i=0;i<N;i++)cnt+=(long)(L[i]/c);
			if(cnt<K){
				r=c;
			}else{
				l=c;
			}
		}
		
		
		Console.WriteLine(c);
		
		
		
	}
	int N;
	double[] L;
	double K;
	public Sol(){
		N=ri();
		L=rda();
		K=rd();
	}




	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(){return Console.ReadLine().Split(' ');}
	static int[] ria(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>int.Parse(e));}
	static long[] rla(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>long.Parse(e));}
	static double[] rda(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>double.Parse(e));}
}