using System;

public class Hello
{
    public static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, int.Parse);
        Array.Sort(a);
        var t = a[1] - a[0];
        if (t == 0) { Console.WriteLine("NO"); goto end; }
        for (int i = 1; i < n-1; i++)
            if (a[i + 1] - a[i] != t) { Console.WriteLine("NO"); goto end; }
        Console.WriteLine("YES");
        end:;
    }
}