#include<bits/stdc++.h>
using namespace std;
using Int = long long;
//INSERT ABOVE HERE
signed main(){
  Int n;
  cin>>n;
  vector<Int> x(n);
  for(Int i=0;i<n;i++) cin>>x[i];
  sort(x.begin(),x.end());
  if(x[1]-x[0]==0){
    cout<<"NO"<<endl;
    return 0;
  }
  for(Int i=1;i<n;i++){
    if(x[1]-x[0]!=x[i]-x[i-1]){
      cout<<"NO"<<endl;
      return 0;
    }
  }
  cout<<"YES"<<endl;
  return 0;
}