class Program
{
    static void Main(string[] args)
    {
        int num = int.Parse(Console.ReadLine()!);
        string[] input = Console.ReadLine()!.Split(' ');
        List<int> numList = new List<int>();

        for (int i = 0; i < input.Length; i++)
        {
            numList.Add(int.Parse(input[i]));
        }
        numList.Sort();

        int criteria = numList[1] - numList[0];
        for (int i = 0; i < numList.Count - 1; i++)
        {
            if (numList[i] == numList[i + 1])
            {
                Console.WriteLine("NO");
                return;
            }
            else if (numList[i + 1] - numList[i] != criteria)
            {
                Console.WriteLine("NO");
                return;
            }
        }
        Console.WriteLine("YES");
    }
}