import java.util.ArrayList;
import java.util.Scanner;
import java.util.TreeSet;

public class Kamo {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		int N = s.nextInt();
		boolean tof = true;
		ArrayList<Integer> x = new ArrayList<>();
		for(int i = 0;i < N;i++){
			int k = s.nextInt();
			if(!x.contains(k)){
				x.add(k);
			}else{
				tof = false;
			}
		}
		s.close();
		if(tof){
			TreeSet<Integer> y = new TreeSet<>();
			y.addAll(x);
			int p = y.pollFirst();
			final int d = y.first() - p;
			p = y.pollFirst();
			while(y.size() != 0){
				if(y.first() -p != d){
					tof = false;
					break;
				}
				p = y.pollFirst();
				
			}
		}
		if(tof){
			System.out.println("YES");
		}else{
			System.out.println("NO");
		}

	}

}