public class Program
{
    public static void Main()
    {
        int num = int.Parse(Console.ReadLine() ?? string.Empty);
        string[] str = (Console.ReadLine() ?? string.Empty).Trim().Split(' ');
        //string str = Console.ReadLine() ?? string.Empty;

        int[] a = new int[str.Length];
        for (int i = 0; i < num; i++)
        {
            a[i] = int.Parse(str[i]);
        }
        Array.Sort(a);

        int b = a[a.Length - 1] - a[a.Length - 2];
        for (int i = a.Length - 2; i >= 1; i--)
        {
            if (b != a[i] - a[i - 1] || a[i] - a[i - 1] == 0)
            {
                Console.WriteLine("NO");
                return;
            }
        }
        Console.WriteLine("YES");
    }
}