using System;

class S25_duck{
  public static int Main(string[] args){
    int n;
    string ans = "YES";
    n = int.Parse(Console.ReadLine());
    int[] duck = new int[n];

    for(int i = 0; i < n; i++){
      duck[i] = int.Parse(Console.ReadLine());
    }

    Array.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-i]){
        ans = "NO";
        break;
      }
    }

    Console.WriteLine(ans);
    return 0;
  }
}