Problem:
Score : 100 points

Problem Statement

Find the number of ways to choose a pair of an even number and an odd number from the positive integers between 1 and K (inclusive). The order does not matter.

Constraints

2\leq K\leq 100

K is an integer.

Input

Input is given from Standard Input in the following format:

K

Output

Print the number of ways to choose a pair of an even number and an odd number from the positive integers between 1 and K (inclusive).

Sample Input 1

3

Sample Output 1

2

Two pairs can be chosen: (2,1) and (2,3).

Sample Input 2

6

Sample Output 2

9

Sample Input 3

11

Sample Output 3

30

Sample Input 4

50

Sample Output 4

625

Solution in Scala (2.11.7) (judge verdict: Accepted)

// A - Pair
// https://abc108.contest.atcoder.jp/tasks/abc108_a

import scala.io.StdIn.readLine

object Main extends App {

  val k = readLine.toInt

  val odd = k / 2
  val even = (k + 1) / 2

  val c = odd * even

  println(c)

}