#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
long to_i(string s)
{
	long ret=0;
	for(char c:s)ret=ret*10+c-'0';
	return ret;
}
long mul(long a,long b,long c)
{
	long ret=0;
	while(b)
	{
		if(b&1)
		{
			ret+=a;
			ret%=c;
		}
		a+=a;
		a%=c;
		b>>=1;
	}
	return ret;
}
long power(long a,long b,long c)
{
	if(b==0)return 1L;
	else if(b%2==0)return power(mul(a,a,c),b/2,c);
	else return mul(a,power(a,b-1,c),c);
}
bool isp(long N)
{
	long s=0,d=N-1;
	while(d%2==0)
	{
		s++;
		d/=2;
	}
	for(long a=2;a<=100&&a<N;a++)
	{
		long ad=power(a,d,N);
		bool flag=ad!=1;
		if(flag)
		{
			for(int r=0;r<s;r++)
			{
				flag=flag&&ad!=N-1;
				ad=mul(ad,ad,N);
			}
		}
		if(flag)return false;
	}
	return true;
}
main()
{
	int N;cin>>N;
	vector<string>A(N);
	for(int i=0;i<N;i++)cin>>A[i];
	sort(A.begin(),A.end());
	if(N==1)
	{
		string s=A[0];
		if(s=="2"||s=="3"||s=="5"||s=="7"||s=="11"||s=="13")
		{
			cout<<s<<endl;
		}
		else
		{
			cout<<-1<<endl;
		}
		return 0;
	}
	long ans=-1;
	do{
		if(to_i(A.back())%2==0)continue;
		string now="";
		for(string a:A)now+=a;
		long X=to_i(now);
		if(isp(X)&&ans<X)ans=X;
	}while(next_permutation(A.begin(),A.end()));
	cout<<ans<<endl;
}