#include<bits/stdc++.h>
using namespace std;
int main(){
int N;
  cin>>N;
  set<int>S;
  for(int i=0;i<N;i++){
  int x;
    cin>>x;
    S.insert(x);
  
  }if(S.size()==N)
    cout<<"YES"<<endl;
  else
    cout<<"NO"<<endl;
    
  
  return 0;
}