import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.stream.Collectors;

public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();

		List<String> list = new ArrayList<>();

		for(int i = 0; i < N; i++) {
			list.add(scan.next());
		}

		List<String> fillteredList = list.stream().distinct().collect(Collectors.toList());

		if(fillteredList.size() == list.size()) {
			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