use std::io::Read;

fn gcd(a: u64, b: u64) -> u64 {
    if b == 0 {
        a
    } else {
        gcd(b, a % b)
    }
}

fn mod_pow(mut x: u64, mut e: u64) -> u64 {
    let mut res: u64 = 1;
    while e > 0 {
        if e % 2 == 1 {
            res = res * x % 10;
        }
        x = x * x % 10;
        e >>= 1;
    }
    res
}

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let mut n: u64 = itr.next().unwrap().parse().unwrap();
    let mut m: u64 = itr.next().unwrap().parse().unwrap();

    let g: u64 = gcd(n, m);
    let mut m2: u64 = 0;
    let mut m5: u64 = 0;
    n /= g;
    m /= g;

    while m % 2 == 0 {
        m /= 2;
        m2 += 1;
    }
    while m % 5 == 0 {
        m /= 5;
        m5 += 1;
    }
    while n % 10 == 0 {
        n /= 10;
    }
    if m != 1 {
        println!("-1");
    } else {
        if m2 > m5 {
            n = (n % 10 * mod_pow(5, m2 - m5)) % 10;
        } else if m5 > m2 {
            n = (n % 10 * mod_pow(2, m5 - m2)) % 10;
        }
        println!("{}", n % 10);
    }
}