import java.util.Scanner;
import java.util.HashSet;
public class Main{
    public static void main(String[]args){
        Scanner scan = new Scanner(System.in);
        int n,flag;
        flag=0;
        n= scan.nextInt();
        HashSet<String>hs = new HashSet<String>();
        for(int i=0;i<n;i++){
            hs.add(scan.next());
        }
        if(n==hs.size()) System.out.printf("YES");
        else System.out.printf("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