fn main() {
    let mut xx = String::new();
    std::io::stdin().read_line(&mut xx).ok();
    let xx: Vec<usize> = xx.split_whitespace().flat_map(str::parse).collect();

    let rem = [0, 2, 1][(xx[0] + xx[1]) % 3];
    let n = (xx[0]..=xx[1]).filter(|&n| n % 3 == rem).count();

    println!("{n}");
}