use std::io::Read;

fn gcd(a: i64, b: i64) -> i64 {
    if b == 0 {
        a
    } else {
        gcd(b, a % b)
    }
}

fn run() {
    let mut s = String::new();
    std::io::stdin().read_to_string(&mut s).unwrap();
    let mut it = s.trim().split_whitespace();
    let n: usize = it.next().unwrap().parse().unwrap();
    let mut ans = 0;
    for s in it {
        let a: i64 = s.parse().unwrap();
        if a > 0 {
            ans = gcd(ans, a * a);
        }
    }
    if ans == 0 {
        println!("-1");
    } else {
        println!("{}", ans);
    }
}

fn main() {
    run();
}