import java.util.*;

class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int range = sc.nextInt();
		Set<String> set = new HashSet<String>();
		for (int i = 0; i < range; i++){
			set.add(sc.next()); 
		}
		if ( set.size() < range){
        	System.out.println("NO");
        }else{
         	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