using System;

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

            for(int x = a - 1; x > 0; x--)
            {
                if (x == a - 1&& b[x] != b[x - 1])
                {
                    k = b[x] - b[x - 1];
                    count++;
                }
                else if (k==b[x] - b[x - 1] && b[x] != b[x - 1])
                {
                    count++;
                }


            }
            if (count == a - 1)
            {
                Console.WriteLine("YES");
            }
            else
            {
                Console.WriteLine("NO");

            }
            
        }
    }
}