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 JavaScript (node.js v5.12) (judge verdict: Accepted)

'use strict'

const main = (input) => {
    const K = parseInt(input)
    if(K % 2 === 0){
        console.log(Math.pow((K / 2), 2))
    } else {
        let base = Math.floor(K / 2)
        console.log(base * (base + 1))
    }
}

main(require('fs').readFileSync('/dev/stdin', 'utf-8'))