import java.security.KeyStore.TrustedCertificateEntry

object Main {

  import java.util.Scanner

  def main(args: Array[String]): Unit = {
    val scanner = new Scanner(System.in)
    val s = scanner.next
    var n = s.toInt
    var sum = 0

    while(n != 0){
      sum += n
      n -= 1
    }

    println(sum)
  }
}