using System;
public class Hello{
    public static void Main(){
        
        string[] s = Console.ReadLine().Split();
        
        for(int i=0;i<s.Length;i++){
            if(s[i].Length>1 || s[i]=="" || s[i]==" "){
                Console.WriteLine("No");
                return;
            }
        }
        
        Console.WriteLine("Yes");
    }
}