package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func stdin() (inputs []string) {
	scanner := bufio.NewScanner(os.Stdin)
	for scanner.Scan() {
		inputs = append(inputs, scanner.Text())
	}
	return
}

// Run is a main process
func Run(inputs []string) string {
	num, _ := strconv.Atoi(inputs[0])
	sum := 0
	for i := 1; i <= num; i++ {
		sum += i
	}
	return fmt.Sprint(sum)
}

func main() {
	p := stdin()
	fmt.Println(Run(p))
}