using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace yuki_406
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.ReadLine();
            var x = scan();
            Array.Sort(x);
            bool z = false;
            int k = x[1] - x[0];
            if (k==0)
            {
                z = true;
            }
            for (int i = 2; i < x.Length; i++)
            {
                if (x[i]-x[i-1]!=k)
                {
                    z = true;
                    break;
                }
            }
            if (z)
            {
                Console.WriteLine("NO");
            }
            else
            {
                Console.WriteLine("YES");
            }
        }
        static int[] scan()
        {
            return
                Array.ConvertAll
                (Console.ReadLine().Split(' '), int.Parse);
        }
    }
}