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

class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
	int n =  sc.nextInt();
	List<String> a = new ArrayList<String>();

	for(int i=0;i<n;i++) {
		a.add(sc.next());
	}

	List<String> b = new ArrayList<String>(new HashSet<>(a));

	int la = a.size();
	int lb = b.size();
	System.out.println(la==lb?"YES":"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