#include<iostream>
#include<algorithm>
#include<iomanip>
using namespace std;

long long int n,k;
double l[1<<18];

bool c(double d)
{
	long long int ans=0;
	for(int i=0;i<n;i++)
	{
		ans+=(int)l[i]/d;
	}
	return ans>=k;
}

int main()
{
	cin>>n;
	for(int i=0;i<n;i++)cin>>l[i];
	cin>>k;

	double a=0.0,b=(double)1e9;

	for(int i=0;i<100;i++)
	{
		double mid=(a+b)/2;
		if(c(mid))a=mid;
		else b=mid;
	}
	cout<<fixed<<setprecision(9)<<a<<endl;
	return 0;
}