#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <cmath>
#include <map>
#include <queue>
#include <iomanip>
#include <set>
#include <tuple>
#define mkp make_pair
#define mkt make_tuple
#define rep(i,n) for(int i = 0; i < (n); ++i)
using namespace std;
typedef long long ll;
const ll MOD=1e9+7;

ll gcd(ll a,ll b){
  return b==0?a:gcd(b,a%b);
}

int main(){
  int N;
  cin>>N;
  vector<ll> A(N);
  rep(i,N) cin>>A[i];

  bool all=true;
  ll g=0;
  rep(i,N){
    if(A[i]!=-1){
      all=false;
      g=A[i];
    }
  }

  if(all){
    cout<<-1<<endl;
    return 0;
  }

  rep(i,N){
    if(A[i]==-1) continue;
    g=gcd(g,A[i]);
  }

  cout<<g*g<<endl;



  return 0;
}