import java.util.*;
 
public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    try {
      int n = sc.nextInt();
      Map<Integer, Integer> cnt = new HashMap<Integer, Integer>();
      boolean ans = true;
      for (int i = 0; i < n; i++) {
        int a = sc.nextInt() - 1;
        if (cnt.containsKey(a)) ans = false;
        cnt.put(a, 1);
      }
      System.out.println(ans ? "YES" : "NO");
    } finally {
      sc.close();
    }
  }
}
/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