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];
            int[] sa = new int[kamo.Length - 1];
            bool flg = true;
            for (int i = 0; i < input2.Length; i++)
            {
                kamo[i] = int.Parse(input2[i]);
            }
            Array.Sort(kamo);
            Array.Reverse(kamo);
            for (int i = 0; i < kamo.Length-1; i++)
            {
                sa[i] = kamo[i] - kamo[i + 1];
            }
            for(int i=0;i<sa.Length-1;i++)
            {
                int sa1 = sa[i];
                int sa2 = sa[i + 1];
                if(sa1!=sa2)
                {
                    flg = false;
                    break;
                }
            }

            for (int i = 0; i < kamo.Length - 1; i++)
            {
                
                for (int j = i + 1; j < kamo.Length; j++)
                {
                    if (Equals(kamo[i], kamo[j]))
                    {
                        flg = false;
                        break;
                    }

                }
                if (flg == false)
                {
                    break;
                }
            }
            if (flg==true)
            {
                Console.WriteLine("YES");
            }
            else
            {
                Console.WriteLine("NO");
            }
        }

    }
}