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

    let mut result: usize = 0;
    for i in a..=b {
        if (a + b + i) % 3 == 0 {
            result += 1;
        }
    }
    println!("{}", result);
}