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 Ruby (2.3.3) (judge verdict: Accepted)

# Your code here!

K = gets.to_i
counter = 0

for i in 1..K
    for j in i..K
        if (i % 2 == 0 && j % 2 != 0) || (i % 2 != 0 && j % 2 == 0)
            counter += 1
        end
    end
end
puts counter