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: Accepted)

import java.io.PrintWriter

val pw = PrintWriter(System.out)

fun main(args : Array<String>) {
    func()
    pw.flush()
}

fun func() {
    val k = nextInt()
    println(when (k % 2) {
        0 -> (k / 2)*(k / 2)
        else -> (k / 2)*(k / 2 + 1)
    })
}

fun next() = readLine()!!
fun nextInt() = next().toInt()

fun println(value : Any) {
    pw.println(value)
}