Module a

ABC 355 A - Who Ate the Cake?

refs: https://atcoder.jp/contests/abc355/tasks/abc355_a

use proconio::input;

fn main() {
    input! {
        a: usize,
        b: usize,
    }

    if a == b {
        println!("-1");
    } else {
        println!("{}", 6 - a - b);
    }
}