use proconio::{fastout, input};

#[fastout]
fn main() {
    input! {
        a: [u8; 4],
    }

    println!("{}", output(solve(a)))
}

fn solve(mut a: Vec<u8>) -> bool {
    a.sort_unstable();
    let a = a;
    a.windows(2).all(|a| a[0] + 1 == a[1])
}

fn output(ans: bool) -> &'static str {
    match ans {
        true => "Yes",
        false => "No",
    }
}