using System;

public class Program {
	public void Solve() {
		Console.ReadLine();  // N
		string[] s = Console.ReadLine().Split(' ');
		
		int[] x = new int[s.Length];
		for (int i = 0; i < x.Length; i++) {
			x[i] = int.Parse(s[i]);
		}
		Array.Sort(x);
		
		int diff = x[1] - x[0];
		for (int i = 2; i < x.Length; i++) {
			if (x[i] - x[i - 1] != diff || x[i] - x[i - 1] == 0 || diff == 0) {
				Console.WriteLine("NO");
				return;
			}
		}
		Console.WriteLine("YES");
	}
	
	public static void Main(string[] args) {
		Program program = new Program();
		program.Solve();
	}
}