
object Main {
  def main(args: Array[String]): Unit = {
    val sc = new java.util.Scanner(System.in)
    val N = sc.nextInt
    var s: Set[Int] = Set()
    var ans: String = "YES"
    for (i <- 0 until N) {
      var a = sc.nextInt
      if (s.contains(a)) ans = "NO"
      else s = s + a
    }
    print(ans)
  }
}
