import java.util.*;
class A{
	static Scanner s = new Scanner(System.in);
	public static void main(String[] args) {
		int in[] = new int[s.nextInt()];
		for(int i=0;i<in.length;i++) {
			in[i]=s.nextInt();
		}
		Arrays.sort(in);
		int f = in[1]-in[0];
		for(int i=2;i<in.length;i++) {
			if((f != in[i]-in[i-1])||(in[i]==in[i-1])) {
				System.out.println("NO");
				return;
			}
		}
		System.out.println("YES");
	}
}