import java.util.Arrays;
import java.util.Scanner;
public class Main {
		public static void main(String[] args) {
			Scanner sc = new Scanner(System.in);
			int N = sc.nextInt();
			int[] l = new int[N];
			for(int i = 0; i < N; i++) {
				l[i] = sc.nextInt();
			}
			Arrays.sort(l);
			int tmp = l[1] - l[0];
			boolean ok = true;
			for(int i = 1; i < N-1; i++) {
				if(tmp != l[i+1] - l[i]) {
					ok = false;
					break;
				}
			}
			if(tmp == 0) ok = false;
			
			System.out.println((ok?"YES":"NO"));
			
		}
}