import java.util.*;
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    List<Integer> a = new ArrayList<>();
    while (sc.hasNext()){
      a.add(sc.nextInt());
    }
    
    boolean ans = (a.size() == new HashSet<>(a).size());
    
    if(ans){
      System.out.println("YES");
    }else{
      System.out.println("NO");
    }

    
    
  }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz