#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#define popcount __builtin_popcount
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;
ll gcd(ll a, ll b){
    if(b==0) return a;
    return gcd(b, a%b);
}
int main()
{
	int n;
    cin>>n;
    bool myon=1;
    ll g=0;
    for(int i=0; i<n; i++){
        ll a; cin>>a;
        if(a==-1) continue;
        myon=0;
        g=gcd(g, a);
    }
    if(myon) cout<<-1<<endl;
    else cout<<g*g<<endl;
	return 0;
}