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

class Program
{
    public void Solve()
    {
        int N = int.Parse(Console.ReadLine());
        int[] X = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
        Array.Sort(X);

        bool isOK = true;

        int diff = X[0] - X[1];
        for (int i = 0; i < X.Length - 1; i++)
        {
            if (X[i] == X[i + 1] || X[i] - X[i + 1] != diff)
            {
                isOK = false;
                break;
            }
        }
        Console.WriteLine(isOK ? "YES" : "NO");
    }

    static void Main()
    {
        var solver = new Program();
        solver.Solve();
    }
}