fn main() {
    let mut ab = String::new();
    std::io::stdin().read_line(&mut ab).ok();
    let ab: Vec<isize> = ab.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let a = ab[0];
    let b = ab[1];

    if b == 0 {
        println!("1");
        return;
    } else if a == 0 {
        println!("-1");
        return;
    }
    if a == -1 {
        println!("2");
    } else {
        println!("-1");
    }
}