#include<iostream>
#include<algorithm>
#include<stdio.h>
#include<stdlib.h>
#include<vector>
#include<string>
#include<sstream>
#include<math.h>
using namespace std;


int main(){

  int n;
  cin >> n;

  vector<int> x(n);
  for(int i=0;i<n;i++) cin >> x[i];

  sort(x.begin(),x.end());

  int dif = abs(x[0]-x[1]);

  for(int i=1;i<n;i++){
    int tmp = abs(x[i-1]-x[i]);
    if( tmp != dif || tmp == 0){
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;

  return 0;
}