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)

function main(input) {
  const K = parseInt(input, 10);
  var a =(K+1)/2
  if(K%2==0){
    console.log((K/2)*(K/2));
  }else{
    console.log(a*(a-1));
  }
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));