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 Scala (2.11.7) (judge verdict: Accepted)

object Main extends App {
  val line = scala.io.StdIn.readLine()
  val num = line.toInt
  println(new candy(num).toInt)

  class candy(n: Int) {
    val num = n
    val result = 0
    def calc(num: Int, r: Int): Int =
      if (num == 0) r else calc(num - 1, r + num)
    def toInt = calc(num, result)
  }
}