#include<bits/stdc++.h>
using namespace std;
using ll = long long;
//using LL = __int128
#define pi pair<ll, ll>
#define M 22
#define N 7111111
ll n, p[M], k, mp[11];
ll tmp[N], tmp1[N], sz, sz1, t[N], pos;
void dfs(int l, int r, ll now, ll mid){
	tmp[++sz] = now;
	for(int i = l ; i <= r ; i++)
		if(now <= mid / p[i])
			dfs(i, r, now * p[i], mid);
}
void dfs1(int l, int r, ll now, ll mid){
	tmp1[++sz1] = now;
	for(int i = l ; i <= r ; i++)
		if(now <= mid / p[i])
			dfs1(i, r, now * p[i], mid);
}
void debug(ll mid, ll ans){
	cerr << mid << " " << sz << " " << sz1 << " " << ans << "\n";
	return;
	for(int i = 1 ; i <= sz ; i++)
		cout << tmp[i] << " \n"[i == sz];
	for(int i = 1 ; i <= sz1 ; i++)
		cout << tmp1[i] << " \n"[i == sz1];
}
void tr(){
	pos = 0;
	for(int i = 1 ; i <= sz ; i++)
		if(tmp[i] != tmp[i - 1])
			t[++pos] = tmp[i];
	sz = pos;
	for(int i = 1 ; i <= pos ; i++)
		tmp[i] = t[i];
}
void tr1(){
	pos = 0;
	for(int i = 1 ; i <= sz1 ; i++)
		if(tmp1[i] != tmp1[i - 1])
			t[++pos] = tmp1[i];
	sz1 = pos;
	for(int i = 1 ; i <= pos ; i++)
		tmp1[i] = t[i];
}
bool check(ll mid){
	ll ans = 0;
	sz = sz1 = 0;
	dfs(1, n / 2, 1, mid);
	dfs1(n / 2 + 1, n, 1, mid);
	//tr();
	//tr1();
	sort(tmp + 1, tmp + 1 + sz);
	sort(tmp1 + 1, tmp1 + 1 + sz1);
	tmp1[sz1 + 1] = mid + 1;
	ll l = sz, r = 1;
	while(l > 0){
		while(tmp[l] <= mid / tmp1[r])
			r++;
		ans += (r - 1);
		//if(mid == 111423952670820829)
		//cerr << l << " " << r << "\n";
		l--;
	}
	//debug(mid, ans);
	return ans >= k;
}
unordered_map<ll, bool> vis;
priority_queue<ll, vector<ll>, greater<ll>> q;

int main(){
	mp[1] = 1;
	mp[0] = -1;
	scanf("%lld", &n);
	for(int i = 1 ; i <= n ; i++){
		scanf("%lld", &p[i]);
	}
	sort(p + 1, p + 1 + n);
	for(int i = 2 ; 2 * i <= n ; i += 2)
		swap(p[i], p[n + 2 - i]);
	//for(int i = 1 ; i <= n ; i++)
		//cout << p[i] << " \n"[i == n];
	ll l = 1, r = 1, ans = 0;
	for(int i = 1 ; i <= 18 ; i++)
		r *= 10;
	scanf("%lld", &k);
	if(k <= -1000000){
		q.push(1);
		ll cnt = 0, u = 0;
		while(cnt < k){
			u = q.top();
			q.pop();
			/*
			if(vis.size() > lim){
				cerr << u << " ";
				clear();
				cerr << vis.size() << " moo\n";
			}
			//*/
			//if(vis.size() % 1000000 == 0)
				//cerr << vis.size() << " " << u << " " << cnt << " moo\n";
			for(int i = 1 ; i <= n ; i++)
				if(u <= r / p[i])
					if(!vis[u * p[i]])
						q.push(u * p[i]), vis[u * p[i]] = true;
			cnt++;
		}
		cout << u;
		return 0;
	}
	if(check(r) && !check(r - 1)){
		printf("%lld", r);
		return 0;
	}
	while(l <= r){
		ll mid = (l + r) >> 1;
		if(check(mid)){
			ans = mid, r = mid - 1;
		}
		else
			l = mid + 1;
	}
	printf("%lld", ans);
	return 0;
}