package main

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

func main() {
	stdin := bufio.NewScanner(os.Stdin)
	stdin.Scan()
	num, err := strconv.Atoi(stdin.Text())
	if err != nil {
		panic(err)
	}
	sum := 0
	for i := 1; i <= num; i++ {
		sum += i
	}
	fmt.Println(sum)
}