use proconio::input;
fn main(){
    input!{
        a:usize,b:usize,c:usize,d:usize,
    }
    let mut x=vec![a,b,c,d];x.sort();
    let mut ans="Yes";
    for i in (0..3){
        if x[i]!=x[i+1]-1{
            ans="No";
        }
    }
    print!("{}",ans);
}