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

class Program
{
	static void Main()
	{
		int n = int.Parse(Console.ReadLine()); //数字1つを読み込み
		int[] xs = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
		Array.Sort(xs);
		int sa = xs[1] - xs[0];
		bool check = true;
		for (int i = 1; i < n; i++)
		{
			if (sa != xs[i] - xs[i - 1])
			{
				check = false;
				break;
			}
		}
		if (sa == 0)
		{
			check = false;
		}

		if (check)
		{
			Console.WriteLine("YES");
		}
		else {
			Console.WriteLine("NO");
		}
	}
}