use std::io::*;

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let mut a: Vec<usize> = (0..4)
        .map(|_| itr.next().unwrap().parse().unwrap())
        .collect();

    a.sort();
    let mut ok = true;
    for i in 0..3 {
        if a[i] + 1 != a[i + 1] {
            ok = false;
        }
    }
    if ok {
        println!("Yes",)
    } else {
        println!("No",)
    }
}