using System;

namespace yukicoder
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] s = Console.ReadLine().Split(' ');
            int[] a = new int[s.Length];
            int count = 0;
            for(int i=0; i < s.Length; i++)
            {
                a[i] = int.Parse(s[i]);
            }
            Array.Sort(a);
            for(int x = 0; x < s.Length-1; x++)
            {
                if (a[x]+1==a[x+1])
                {
                    count++;
                }
            }

            if (count == s.Length - 1)
            {
                Console.WriteLine("Yes");
            }
            else
            {
                Console.WriteLine("No");
            }

            
            
        }
    }
}