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

namespace YukiCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            int nn = int.Parse(Console.ReadLine());
            var va = Console.ReadLine().Split().Select(int.Parse).OrderBy(n=>n).ToArray();
            var vb = va.Skip(1).Select((n, i) => n - va[i]);
            int max = vb.Max();
            int min = vb.Min();
            var ss = max != min ? "NO" : max == 0 ? "NO" : "YES";
            Console.WriteLine(ss);
            Console.ReadLine();
        }
    }
}