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: Accepted)

#pragma GCC diagnostic ignored "-Wunused-result"

#include <stdio.h>

int main(void) {
  int K;
  int ret;
  
  scanf("%d",&K);

  if (K%2 == 0) { // Even
    ret = (K/2)*(K/2);
  } else { // Odd
    ret = (K/2+1)*(K/2);
  }
  
  printf("%d\n",ret);
  return 0;

}