import java.util.*;

public class Exercise159 {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] array = new int[n];
    for(int i = 0; i < n; i++){
      array[i] = sc.nextInt();
    }
    Arrays.sort(array);
    int a = array[n - 1] - array[n - 2];
    if(a == 0){
      System.out.println("NO");
      return;
    }
    for(int i = n - 1; i > 0; i--){
      int b = array[i] - array[i - 1];
      if(b != a){
        System.out.println("NO");
        return;
      }
    }
    System.out.println("YES");
  }
}