#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <algorithm>
//---------------------------
using namespace std;
//---------------------------
#define REP(i,n) for(int i = 0; i < (n); i++)
#define P(x) cout << (x) << "\n"
//---------------------------


int main(){
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);



  long n;cin>>n;
  vector<long long> v(n);
  REP(i,n){cin >> v[i];}
  sort(v.begin(),v.end());
  if (v[1] -v[0] == 0) {
    P("NO");
  }else{
  REP(i,n - 1){
    if (v[i+1]-v[i] != v[1]-v[0]) {
      P("NO");
      break;
    }else if (i == n-2) {
      P("YES");
      break;
    }
  }
}

  return 0;
}