fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let a: isize = itr.next().unwrap().parse().unwrap();
    let b: isize = itr.next().unwrap().parse().unwrap();
    
    let mut ans = 0;
    for i in a..=b {
        if (a + b + i) % 3 == 0 { ans += 1};
    }

    println!("{}", ans);
}