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)

// parameter "input" gets all data
function Main(input) {
	// the first line is assigned to input[0], the second line is assigned to input[1] similarly.
	var n = parseInt(input);
	if(n%2==1)
		console.log(parseInt((n-1)*(n+1)/4));
	else
		console.log(parseInt((n*n)/4));
}
// Don't edit this line!
//Main(require("fs").readFileSync(__dirname+'/in.txt', "utf8"));
Main(require('fs').readFileSync('/dev/stdin', 'utf8'));