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"); 
        }
	}
}	 import java.util.*; util.* java 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"); 
        }
	}
} 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"); 
        }
	} main {
		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"); 
        }
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int range = sc.nextInt(); range sc.nextInt() sc.nextInt sc Set<String> set = new HashSet<String>(); set new HashSet<String>() for (int i = 0; i < range; i++){
			set.add(sc.next()); 
		} int i = 0; int i = 0; i 0 i < range i range i++ i++ i {
			set.add(sc.next()); 
		} {
			set.add(sc.next()); 
		} set.add(sc.next()) set.add set sc.next() sc.next sc if ( set.size() < range){
        	System.out.println("NO");
        }else{
         	System.out.println("YES"); 
        } set.size() < range set.size() set.size set range {
        	System.out.println("NO");
        } System.out.println("NO") System.out.println System.out System System.out "NO" {
         	System.out.println("YES"); 
        } System.out.println("YES") System.out.println System.out System System.out "YES" String[] args args
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"); 
        }
	}
}	