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

int64_t gcd(int64_t a, int64_t b){
    return b==0 ? a : gcd(b, a%b);
}

int main(){
    int N;
    cin >> N;
    int64_t ans = 0;
    for(int i=0; i<N; i++){
        int a;
        cin >> a;
        if(a > 0) ans = gcd(ans, a);
    }
    if(ans == 0){
        ans = -1;
    }else{
        ans *= ans;
    }
    cout << ans << endl;
    return 0;
}