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 Kotlin (1.0.0) (judge verdict: Runtime Error)

package AtCoder

import java.util.Scanner;

fun main(args: Array<String>) {
	val sc = Scanner(System.`in`)
	val num = Integer.parseInt(sc.nextLine())
	sc.close()
	val od: Int = num / 2 + num % 2
	val ev: Int = num / 2
	println(od * ev)
}