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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>

int
main(int argc, char *argv[])
{
  int x[4], y[4];
  scanf("%d%d%d%d",&x[0], &y[0], &x[1], &y[1]);
  
  x[2] = x[1] + y[0] - y[1];
  y[2] = -x[0] + x[1] + y[1];
  x[3] = x[0] + y[0] - y[1];
  y[3] = x[1] - x[0] + y[0];
  
  printf("%d%d%d%d", x[2], y[2], x[3], y[3]);
  
  return 0;
}