#include<iostream>
using namespace std;
int gcd(int a,int b){return b?gcd(b,a%b):a;}
int N,A;
main()
{
	cin>>N;
	int X=0;
	for(int i=0;i<N;i++)
	{
		cin>>A;
		if(A>0)X=gcd(X,A);
	}
	cout<<(X==0?-1:(long)X*X)<<endl;
}