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

class S25_duck{
  public static void main(String[] args){
      int n;
      String ans = "YES";
      Scanner sc = new Scanner(System.in);

      n = sc.nextInt();
      int[] duck = new int[n];

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

      Arrays.sort(duck);

      int a = duck[1] - duck[0];
      for(int i = 2; i < n; i++){
        if((duck[i] - duck[i-1]) != a || duck[i] == duck[i-1]){
          ans = "NO";
          break;
        }
      }
      System.out.println(ans);
  }
}