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

public class Kamo {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		int N = s.nextInt();
		boolean tof = true;
		int[] x = new int[N];
		for(int i = 0;i < N;i++){
			x[i] = s.nextInt();
		}
		s.close();
		Arrays.sort(x);
		final int d = x[1]-x[0];
		for(int i = 1;i < N;i++){
			if(x[i] == x[i-1] || x[i]-x[i-1] != d){
				tof =false;
				break;
			}
		}
		if(tof){
			System.out.println("YES");
		}else{
			System.out.println("NO");
		}

	}

}