import java.io.{BufferedOutputStream, BufferedReader, InputStreamReader, PrintWriter}

import scala.annotation.tailrec

object Main {
  def main(args: Array[String]): Unit = {
    val in = new BufferedReader(new InputStreamReader(System.in))
    val out = new PrintWriter(new BufferedOutputStream(System.out))
    val n = in.readLine().toInt

    def candies(n: Int): Int = {
      @tailrec
      def inner(acc: Int, n: Int): Int = {
        if (n == 0) {
          acc
        } else {
          inner(acc + n , n - 1)
        }
      }
      inner(0, n)
    }

    out.println(candies(n))

    out.flush()
  }
}
