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

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