import java.util.Scanner

object test {
  def main(args: Array[String]): Unit = {
    println("1+...+N, N?")
    val sc = new Scanner(System.in)
    val a = sc.nextInt
    var x = 0

    for (c <- 0 to a) {
      x = x + c
    }

    println(x)
  }
}