import java.util.*;

public class Main{
  public static void main(String[] args){
    int i, diff;
    Scanner sc = new Scanner(System.in);
    int num = sc.nextInt();
    int[] array = new int[num];
    for(i=0;i<num;i++){
      array[i] = sc.nextInt();
    }
    Arrays.sort(array);
    diff = array[1] - array[0];
    for(i=1;i<num;i++){
      if(diff != array[i] - array[i-1])break;
      if(i==num-1)System.out.println(diff!=0?"YES":"NO");
    }
    if(i!=num)System.out.println("NO");
  }
}