using System;
using System.Linq;

public class Program
{
    public static void Main(string[] args)
    {
        var n = int.Parse(Console.ReadLine());
        var input = Console.ReadLine().Split(' ').Select(x => ulong.Parse(x)).OrderBy(x => x).ToArray();

        var dist = input[1] - input[0];
        for (int i=0; i < input.Length - 1 ; i++)
        {
            if (input[i] == input[i + 1]) { Console.WriteLine("NO"); return; }
            else
            {
                if (input[i+1] - input[i] != dist) { Console.WriteLine("NO"); return; }
            }
        }
        Console.WriteLine("YES");
    }
}