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

namespace yukicoderTest
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = Console.ReadLine();
            string[] input2 = Console.ReadLine().Split(' ');
            int n = int.Parse(input);
            int[] kamo = new int[input2.Length];
            bool flg = true;
            for(int i=0;i<kamo.Length;i++)
            {
                kamo[i] = int.Parse(input2[i]);
            }
            Array.Sort(kamo);
            Array.Reverse(kamo);
            int sa = kamo[0] - kamo[1];
            
            for (int i = 0; i < kamo.Length - 1; i++)
            {
                if (sa != kamo[i] - kamo[i + 1])
                {
                    flg = false;
                    break;
                }
                else if(sa==0)
                {
                    flg = false;
                    break;
                }
            }
            if(flg==true)
            {
                Console.WriteLine("YES");
            }
            else
            {
                Console.WriteLine("NO");
            }
        }

    }
}