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

    if a < b {
        println!("{}", b - 2);
    } else {
        println!("{}", 2000000000 - b - 1);
    }
}