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 Python (3.8.2) (judge verdict: Accepted)

#k = int(input())
#s = input()
#a, b = map(int, input().split())
#s, t = map(str, input().split())
#l = list(map(int, input().split()))
#l = [list(map(int,input().split())) for i in range(n)]
#a = [list(input()) for _ in range(n)]

K = int(input())
ans = 0
for i in range(1, K+1):
    for j in range(i+1, K+1):
        if (i % 2 == 0 and j % 2 != 0):
            ans += 1
        elif (i % 2 != 0 and j % 2 == 0):
            ans += 1
print(ans)