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

public class Test
{
	public static void Main()
	{
		var N = int.Parse(Console.ReadLine());
		var x = Console.ReadLine()
				.Split(' ')
				.Select(n => int.Parse(n))
				.ToList();
		x.Sort();
		var d = new List<int>();
		
		for(int i = 0; i < x.Count - 1; i++) d.Add(x[i + 1] - x[i]);
		string ans = "YES";
		for(int j = 0; j < d.Count; j++)
		{
			if(d[0] == 0)
			{
				ans = "NO";
				break;
			}
			if(d[j] != d[0] || d[j] == 0)
			{
				ans = "NO";
				break;
			}
		}
		Console.WriteLine(ans);
	}
}