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

public class Test {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt(), s;
		int[] t = new int[n];
		for (int i = 0; i < n; i++) {
			t[i] = sc.nextInt();
		}
		Arrays.sort(t);
		s = t[1] - t[0];
		if (s == 0) {
			System.out.println("NO");
			return;
		}
		for (int i = 2; i < n; i++) {
			if (s != t[i] - t[i - 1]) {
				System.out.println("NO");
				return;
			}
		}
		System.out.println("YES");
	}
}