use std::io::Read;

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 n: u128 = itr.next().unwrap().parse().unwrap();
    let m: u128 = itr.next().unwrap().parse().unwrap();

    for i in 0..18 {
        let num: u128 = n * 10u128.pow(i);
        if num % m == 0 {
            let mut ans = num / m;
            while ans % 10 == 0 {
                ans /= 10;
            }
            println!("{}", ans % 10);
            return;
        }
    }
    println!("-1");
}