#include <bits/stdc++.h>
using namespace std;
 
int main(){
  int N; cin>>N;
  vector<long long> birds(N);
  for(int i=0;i<N;i++){
      cin>>birds[i];
  }
  sort(birds.begin(),birds.end());
  bool frag=true;
  for(int i=0;i<N-1;i++){
      if(birds[i]==birds[i+1]){
          frag=false;
          goto END;
      }
  }
  for(int i=0;i<N-2;i++){
      if(birds[i+2]-birds[i+1]!=birds[i+1]-birds[i]){
         frag=false;
          break;
      }
  }
  END:
  if(frag){
      cout<<"YES"<<endl;
  }
  else{
      cout<<"NO"<<endl;
  }
}