'use strict'

const main = input => {
	const args = input.split('\n').map(arg => arg.split(' '))
	const n = parseInt(args[0][0], 10)
	let sum = 0

	for (let i = 1; i <= n; i++) {
		sum += i
	}

	console.log(sum)
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'))