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 (3.4.3) (judge verdict: Accepted)

import sys
import copy
import math
import bisect
import pprint
import bisect
from functools import reduce
from copy import deepcopy
from collections import deque

def lcm(x, y):
    return (x * y) // math.gcd(x, y)

if __name__ == '__main__':
    a = [int(i) for i in input().split()]

    if a[0] %2 ==1:
        print((a[0]//2)*(a[0]//2+1))
    else:
        print((a[0]//2)*(a[0]//2))