#include<bits/stdc++.h>
using namespace std;

template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

template<typename T> void drop(const T &x){cout<<x<<endl;exit(0);}

struct FastIO{
  FastIO(){
    cin.tie(0);
    ios::sync_with_stdio(0);
  }
}fastio_beet;

//INSERT ABOVE HERE
signed main(){
  int n;
  cin>>n;
  assert(1<=n && n<=2e5);

  vector<int> as(n);
  for(int i=0;i<n;i++) cin>>as[i];
  for(int a:as)
    assert((1<=a && a<=1e9) || a==-1);

  vector<int> bs;
  for(int a:as)
    if(a>0) bs.emplace_back(a);

  if(bs.empty()) drop(-1);

  int g=bs[0];
  for(int b:bs)
    g=__gcd(g,b);

  cout<<(long long)g*g<<endl;
  return 0;
}