import java.util.*;
 
public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
        HashSet hs = new HashSet();
        for(int i = 0; i < n; i++){
        	hs.add(sc.next());
        }
        if(n == hs.size()){
        	System.out.println("YES");
        }else{
        	System.out.println("NO");
        }
    }
} import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
        HashSet hs = new HashSet();
        for(int i = 0; i < n; i++){
        	hs.add(sc.next());
        }
        if(n == hs.size()){
        	System.out.println("YES");
        }else{
        	System.out.println("NO");
        }
    }
} Main public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
        HashSet hs = new HashSet();
        for(int i = 0; i < n; i++){
        	hs.add(sc.next());
        }
        if(n == hs.size()){
        	System.out.println("YES");
        }else{
        	System.out.println("NO");
        }
    } main {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
        HashSet hs = new HashSet();
        for(int i = 0; i < n; i++){
        	hs.add(sc.next());
        }
        if(n == hs.size()){
        	System.out.println("YES");
        }else{
        	System.out.println("NO");
        }
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc HashSet hs = new HashSet(); hs new HashSet() for(int i = 0; i < n; i++){
        	hs.add(sc.next());
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
        	hs.add(sc.next());
        } {
        	hs.add(sc.next());
        } hs.add(sc.next()) hs.add hs sc.next() sc.next sc if(n == hs.size()){
        	System.out.println("YES");
        }else{
        	System.out.println("NO");
        } n == hs.size() n hs.size() hs.size hs {
        	System.out.println("YES");
        } System.out.println("YES") System.out.println System.out System System.out "YES" {
        	System.out.println("NO");
        } System.out.println("NO") System.out.println System.out System System.out "NO" String[] args args public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
        HashSet hs = new HashSet();
        for(int i = 0; i < n; i++){
        	hs.add(sc.next());
        }
        if(n == hs.size()){
        	System.out.println("YES");
        }else{
        	System.out.println("NO");
        }
    }
} public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
        HashSet hs = new HashSet();
        for(int i = 0; i < n; i++){
        	hs.add(sc.next());
        }
        if(n == hs.size()){
        	System.out.println("YES");
        }else{
        	System.out.println("NO");
        }
    }
} Main
import java.util.*;
 
public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
        HashSet hs = new HashSet();
        for(int i = 0; i < n; i++){
        	hs.add(sc.next());
        }
        if(n == hs.size()){
        	System.out.println("YES");
        }else{
        	System.out.println("NO");
        }
    }
}