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

class Program
{
    static void Main(string[] args)
    {
        int n = int.Parse(Console.ReadLine());
        int[] a = Console.ReadLine().Split().Select(v => int.Parse(v)).ToArray();
        Array.Sort(a);
        string ans = "YES";

        if (Judge(a))
        {
            for (int i = 0; i < n - 2; i++)
            {
                if (a[i] - a[i + 1] != a[i + 1] - a[i + 2])
                {
                    ans = "NO";
                    break;
                }
            }
        }
        else
        {
            ans = "NO";
        }

        Console.WriteLine(ans);
        Console.Read();
    }

    static bool Judge(int[] a)
    {
        int len = a.Length;

        for (int i = 0; i < len - 1; i++)
        {
            if (Array.LastIndexOf(a, a[i]) != i)
            {
                return false;
            }
        }
        return true;
    }
}