fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let mut abcd: Vec<usize> = s.trim().split_whitespace()
        .map(|x| x.parse().unwrap()).collect();

    abcd.sort();

    let mut ans = false;
    for x in abcd.windows(2) {
        if x[0] + 1 == x[1] { ans = true }
        else { ans = false }               
    };

    println!("{}",
        if ans { "Yes" }
        else { "No" }
    );
}