Problem:
Score : 100 points

Problem Statement

There are N children in AtCoder Kindergarten. Mr. Evi will arrange the children in a line, then give 1 candy to the first child in the line, 2 candies to the second child, ..., N candies to the N-th child. How many candies will be necessary in total?

Constraints

1≦N≦100

Input

The input is given from Standard Input in the following format:

N

Output

Print the necessary number of candies in total.

Sample Input 1

3

Sample Output 1

6

The answer is 1+2+3=6.

Sample Input 2

10

Sample Output 2

55

The sum of the integers from 1 to 10 is 55.

Sample Input 3

1

Sample Output 3

1

Only one child. The answer is 1 in this case.

Solution in OCaml (4.02.3) (judge verdict: Accepted)

open Batteries
open Printf
let () =
  let n = Scanf.scanf "%d " (fun a -> a) in

  let rec aux n res =
    if n = 0 then res else
      aux (n-1) (res+n)
  in

  Printf.printf "%d\n" @@
  aux n 0