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 Julia (0.5.0) (judge verdict: Runtime Error)

function main()
	d = split(readline(STDIN))
	xone = parse(Int64, d[1])
	yone = parse(Int64, d[2])
	xtwo = parse(Int64, d[3])
	ytwo = parse(Int64, d[4])
	xthr = xtwo + yone - ytwo
	ythr = ytwo - xone + xtwo
	xfou = xthr + xone - xtwo
	yfou = ythr + yone - ytwo
	println(xthr, " ", ythr, " ", xfou, " ", yfou, " ")
end

main()