//
//  main.swift
//  Atcoder
//
//  Created by Louis Joe Shen on 2020/9/26.
//  Copyright © 2020 Louise Joe Shen. All rights reserved.
//

import Foundation

var input = readLine()!.split(separator: " ")

var N = Int(input[0])!

var sum = 0

for i in 1 ... N{
    sum += i
}

print(sum)
