import scala.collection.mutable._

object Main extends App {
	val sc = new java.util.Scanner(System.in)
	val pw = new java.io.PrintWriter(System.out)
	
	val n = sc.nextInt
	val a = Seq.fill(n)(sc.nextInt)
	
	pw.println(if (a.distinct.size == n) "YES" else "NO")
	pw.flush()
}