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

    abcd.sort();
    if abcd[0] + 1 == abcd[1] && abcd[1] + 1 == abcd[2] && abcd[2] + 1 == abcd[3] {
        println!("Yes");
    } else {
        println!("No");
    }
}