#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using pii = pair<int, int>;
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define repr(i, n) for (int i = (int)(n - 1); i >= 0; --i)

int gcd(int x, int y) {
    if (x > y) swap(x, y);
    return x == 0 ? y : gcd(y % x, x);
}
int main() {
    int n;
    cin >> n;
    vi a(n);
    rep(i, n) cin >> a[i];
    int r = 0;
    rep(i, n) {
        if (a[i] >= 0) r = gcd(r, a[i]);
    }
    cout << (r == 0 ? -1 : (ll)r * r) << endl;
    return 0;
}