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