use std::f32;
use std::io::stdin;

fn get_line() -> String {
    let mut line = String::new();
    stdin().read_line(&mut line).ok();
    line
}

fn main() {
    let line = get_line();
    let line: Vec<&str> = line.split_whitespace().collect();

    let a: i16 = line[0].parse().unwrap();
    let b: i16 = line[1].parse().unwrap();

    let mut result = 0;
    for i in a..b + 1 {
        let sum = a + b + i;
        let average = sum as f32 / 3.0;
        if average.fract() == 0.0 {
            result += 1;
        }
    }
    println!("{}", result);
}