fn gcd(n: usize, m: usize) -> usize {
    if m == 0 { return n; }
    gcd(m, n % m)
}

fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    let mut m = String::new();
    std::io::stdin().read_line(&mut m).ok();
    let m: usize = m.trim().parse().unwrap();

    let gcdval = gcd(n, m);
    let n = n / gcdval;
    let m = m / gcdval;
    let mut tempm = m;
    let mut cnt2 = 0usize;
    let mut cnt5 = 0usize;
    while tempm % 2 == 0 { tempm /= 2; cnt2 += 1; }
    while tempm % 5 == 0 { tempm /= 5; cnt5 += 1; }
    if tempm > 1 {
        println!("-1");
    } else if m == 1 {
        println!("{}", n.to_string().chars().rev().filter(|&c| c != '0').nth(0).unwrap());
    } else {
        if cnt5 == cnt2 {
            println!("{}", n.to_string().chars().rev().filter(|&c| c != '0').nth(0).unwrap());
        } else if cnt5 > cnt2 {
            let starts = vec![0,2,2,6,4,1,6,4,8,8];
            let mapping = vec![2,4,8,6];
            if n % 2 == 1 {
                cnt5 -= 1;
            }
            let idx = (0..4).filter(|&v| mapping[v] == starts[n%10]).nth(0).unwrap();
            println!("{}", mapping[(idx+cnt5-cnt2)%4]);
        } else {
            println!("5");
        }
    }
}