object Main extends App
{
  val input : List[Int] = List(1, -3, 4, 2, -1)

  var w : (Boolean, Int) =
    input.foldLeft((false, 0)) { case (acc: (Boolean, Int), v: Int) =>
      if (v * acc._2 > 0) (true, v)
      else (acc._1, v)
    }

  if (w._1) print("YES")
  else print("NO")
}