using System;
using System.Linq;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] line = Console.ReadLine().Trim().Split(' ').Select(int.Parse).ToArray();
            Array.Sort(line);
            Console.WriteLine(line[0]+1 == line[1] && line[1]+1 == line[2] && line[2] +1== line[3]  ? "Yes" : "No");
        }
    }
}