package main

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

func main() {
	sc := bufio.NewScanner(os.Stdin)
	s := ""
	sc.Scan()
	s = sc.Text()
	n, _ := strconv.Atoi(s)
	sum := 0
	for i := 1; i <= n; i++ {
		sum += i
	}
	fmt.Println(sum)
}