using System;

public class Hello
{
    static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, int.Parse);
        Array.Sort(a);
        Console.WriteLine(a[0] + 1 == a[1] && a[1] + 1 == a[2] && a[2] + 1 == a[3] ? "Yes" : "No");
    }
}