import scala.collection.mutable
import scala.io.StdIn._

object Main extends App {

  val count = readInt
  val numList = readLine.split(" ").map(_.toInt)


  val set = mutable.Set.empty[Int]
  var result = "YES"

  numList.foreach { num =>
    if (set.contains(num)) {
      result = "NO"
    }
    set.add(num)
  }

  println(result)
}
