#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>
#include<bitset>

using namespace std;

#define int long long
#define endl "\n"

constexpr long long INF = (long long)1e18;
constexpr long long MOD = 1'000'000'007; 

string yn(bool f){return f?"Yes":"No";}
string YN(bool f){return f?"YES":"NO";}



signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(10);
	
	int con = 0;
	int gcd = 0;
	int N;
	vector<int> A;
	
	cin>>N;
	
	A.resize(N);
	
	for(int i = 0; i < N; i++){
		cin>>A[i];
		if(A[i] == -1) con++;
		else gcd = __gcd(gcd, A[i]);
	}
	
	if(con == N) cout<<-1<<endl;
	else cout<<gcd*gcd<<endl;
	
	/*
	for(int k = 0; k < N; k++){
		vector<int> con(N);
		int sum = 0, sum2 = 0;
		
		for(int i = 0; i < N; i++){
			for(int j = 0; j < N; j++){
				if((i&j) == k) {
					// cout<<"k = "<<k<<" <> "<<i<<" "<<j<<endl;
					// cout<<bitset<10>(k)<<endl;
					// cout<<bitset<10>(i)<<endl;
					// cout<<bitset<10>(j)<<endl;
					sum2 += A[i] * A[j];
					con[i]++;
					con[j]++;
					sum += 2;
				}
			}
			
		}
		
		gcd = __gcd(sum2, gcd);
		
		cout<<"k = "<<k<<" sum = "<<sum<<" sum2 = "<<sum2<<endl;
		for(int i = 0; i < N; i++){
				cout<<con[i]<<" ";
			}
			cout<<endl;
		cout<<endl;
	}
	*/
	
	
	// cout<<gcd<<endl;
	
	return 0;
}