#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; }