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 Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Data.List
import Control.Monad

day :: [String]
day = ["SUN", "MON", "TUE", "WED", "WED", "THU", "FRI", "SAT"]

main = print =<< ((pure (\n -> div (n * (n + 1)) 2)) <*> getInt)

getInt :: IO Int 
getInt = (pure read) <*> getLine