use std::io::{Read, stdin};

fn main() {
    let mut buf = String::new();
    stdin().read_to_string(&mut buf).unwrap();
    let mut tok = buf.split_whitespace();
    let mut get = || tok.next().unwrap().parse::<i64>().unwrap();
    let a = get();
    let b = get();
    let mut ans = 0;
    for i in a..b+1 {
        let sum = a + b + i;
        if sum % 3 == 0 {
            ans += 1;
        }
    }
    println!("{}", ans);
}