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[] x = new int[n];
		for (int i = 0; i < x.length; i++) {
			x[i] = sc.nextInt();
		}

		Arrays.sort(x);
		for(int i = 0 ; i < n - 1 ; i++) {
			if(x[i] == x[i + 1]) {
				System.out.println("NO");
				return;
			}
		}
		int sub = x[1] - x[0];
		for(int i =  1 ; i < n - 1 ; i++) {
			if(x[i + 1] - x[i] != sub) {
				System.out.println("NO");
				return;
			}
		}
		System.out.println("YES");
	}
}