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: Runtime Error)

team=input()
x=team[0]
flag=0
d=0
for i in range(len(team))
   if team[i]==x:
       flag+=1
   else:
        x=team[i]
        flag=0
   if flag==7:
       print("yes")
       d=1
       break
if d=0:
    print("no")