/**
	Author: 丘成桐(囯内)
**/
#include<bits/stdc++.h>
#define int long long
using namespace std;
void ts(){cout<<"IAKIOI\n";}
int n,k,mid,res;
int a[20];
vector<int> v;
void dfs1(int x,int s){
	if(x==n/2+1){
		v.push_back(s);
		return;
	}
	for(int i=0;s<=(int)1e18;i++){
		dfs1(x+1,s);
		if(s<=(int)1e18/a[x])s*=a[x];
		else break;
	}
}
void dfs2(int x,int s){
	if(x==n+1){
		//<=mid/s
		//cout<<s<<"\n";
		int l=0,r=(int)v.size()-1;
		int qr=-1;
		while(l<=r){
			int p=(l+r)/2;
			if(v[p]<=mid/s){qr=p;l=p+1;}
			else r=p-1;
		}
		res+=qr+1;
		return;
	}
	for(int i=0;;i++){
		dfs2(x+1,s);
		if(s<=mid/a[x])s*=a[x];
		else break;
	}
}
bool check(int x){
	mid=x;
	//能组成的 <=x 的数的个数 >=k.
	res=0;
	dfs2(n/2+1,1);
	return res>=k;
}
signed main(){
	cin>>n;
	for(int i=1;i<=n;i++)cin>>a[i];
	cin>>k;
	sort(a+1,a+n+1);
	dfs1(1,1);
	sort(v.begin(),v.end());
	int l=1,r=1e18;
	int rr=0;
	while(l<=r){
		int mid=(l+r)/2;
		if(check(mid)){
			rr=mid,r=mid-1;
		}
		else l=mid+1;
	}
	cout<<rr<<"\n";
	return 0;
}