import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		
		long[] arr = new long[N];
		for(int i = 0; i < N; i++){
			arr[i] = sc.nextLong();
		}
		
		Arrays.sort(arr);
		
		final long diff = arr[1] - arr[0];
		if(diff == 0){
			System.out.println("NO");
		}else{
			for(int i = 2; i < N; i++){
				if(diff != arr[i] - arr[i - 1]){
					System.out.println("NO");
					return;
				}
			}
			
			System.out.println("YES");
		}
		
	}

}