import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int []x = new int[N];
		for(int i = 0; i < N; i++) {
			x[i] = scan.nextInt();
		}
		scan.close();
		Arrays.sort(x);
		int k = x[1] - x[0];
		if(k == 0) {
			System.out.println("NO");
			System.exit(0);
		}
		for(int i = 1; i < N - 1; i++) {
			if(k != x[i+1] - x[i]) {
				System.out.println("NO");
				System.exit(0);
			}
		}
		System.out.println("YES");

	}
}