import java.util.*;

class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    sc.next();
    Set<String> set = new HashSet<>();
    while (sc.hasNext()) {
      if (!set.add(sc.next())) {
        System.out.println("NO");
        return;
      }
    }
    System.out.println("YES");
  }
} import java.util.*; util.* java class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    sc.next();
    Set<String> set = new HashSet<>();
    while (sc.hasNext()) {
      if (!set.add(sc.next())) {
        System.out.println("NO");
        return;
      }
    }
    System.out.println("YES");
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    sc.next();
    Set<String> set = new HashSet<>();
    while (sc.hasNext()) {
      if (!set.add(sc.next())) {
        System.out.println("NO");
        return;
      }
    }
    System.out.println("YES");
  } main {
    Scanner sc = new Scanner(System.in);
    sc.next();
    Set<String> set = new HashSet<>();
    while (sc.hasNext()) {
      if (!set.add(sc.next())) {
        System.out.println("NO");
        return;
      }
    }
    System.out.println("YES");
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) sc.next() sc.next sc Set<String> set = new HashSet<>(); set new HashSet<>() while (sc.hasNext()) {
      if (!set.add(sc.next())) {
        System.out.println("NO");
        return;
      }
    } sc.hasNext() sc.hasNext sc {
      if (!set.add(sc.next())) {
        System.out.println("NO");
        return;
      }
    } if (!set.add(sc.next())) {
        System.out.println("NO");
        return;
      } !set.add(sc.next()) set.add(sc.next()) set.add set sc.next() sc.next sc {
        System.out.println("NO");
        return;
      } System.out.println("NO") System.out.println System.out System System.out "NO" return; 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);
    sc.next();
    Set<String> set = new HashSet<>();
    while (sc.hasNext()) {
      if (!set.add(sc.next())) {
        System.out.println("NO");
        return;
      }
    }
    System.out.println("YES");
  }
}