import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		int n = sc.nextInt();
        boolean ans = true;
        List<String> list = new ArrayList<String>();
        for(int i = 0;i < n;i++){
          list.add(sc.next());
        }
        
        

        ans = (list.size() == new HashSet<>(list).size());
        if(ans == false){
          System.out.println("NO");
          return;
          }
        System.out.println("YES");
    }
}
/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