import java.util.Scanner

object Main extends App {
  val sc = new Scanner(System.in)
  val ans = fact(sc.nextInt)

  def fact(num: Int): Int = num match {
    case n if n == 0 => 0
    case n if n == 1 => 1
    case n => n + fact(n - 1)
  }

  println(ans)
}
