import java.util.Arrays;
import java.util.Scanner;
public class Main{
	private static Scanner sc=new Scanner(System.in);
	public static void main(String args[])throws Exception{
		int n=sc.nextInt();
		int are[]=new int[n];
		for(int i=0;i<are.length;i++)are[i]=sc.nextInt();
		Arrays.sort(are);
		int sa=are[1]-are[0];
		for(int i=0;i<are.length-1;i++){
			int now=are[i+1]-are[i];
			if(now != sa || now == 0){
				System.out.println("NO");
				return;
			}
		}System.out.println("YES");
	}
}