import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Scanner;

public class Main {
	public static void main(String[] args)throws Exception {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		String[] str = new String[N];
		for(int i =0;i<N;i++) {
			str[i]=sc.next();
		}

	     List<String> listA = new ArrayList<String>(Arrays.asList(str));
	     List<String> listB = new ArrayList<String>(new HashSet<>(listA));

	    if(listA.size()==listB.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