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] == line[1] + 1 && line[1] == line[2] + 1 && line[2] == line[3] ? "Yes" : "No");
        }
    }
}