#include<bits/stdc++.h>
using namespace std;
typedef unsigned long long int ull;
typedef long long int ll;
typedef pair<ll,ll> pll;
typedef long double D;
//typedef complex<D> P;
#define F first
#define S second
const ll MOD=1000000007;
//const ll MOD=998244353;

template<typename T,typename U>istream & operator >> (istream &i,pair<T,U> &A){i>>A.F>>A.S; return i;}
template<typename T>istream & operator >> (istream &i,vector<T> &A){for(auto &I:A){i>>I;} return i;}
template<typename T,typename U>ostream & operator << (ostream &o,const pair<T,U> &A){o<<A.F<<" "<<A.S; return o;}
template<typename T>ostream & operator << (ostream &o,const vector<T> &A){int i=A.size(); for(auto &I:A){o<<I<<(--i?" ":"");} return o;}

ll gcd(ll a,ll b){
  while(b!=0){a%=b; swap(a,b);}
  return a;
}

int main(){
  ll N,ans=0;
  cin>>N;
  for(int i=0;i<N;i++){
    ll a;
    cin>>a;
    if(a!=-1){ans=gcd(ans,a);}
  }
  cout<<(ans==0?-1LL:ans*ans)<<endl;
  
  return 0;
}