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)

#include <stdio.h>

int main(int argc, char const *argv[]) {
	char str[101];
	int n, m;
	int ans;

	fgets(str, 100, stdin);
	sscanf(str, "%d\n", &n);

	if (n % 2 == 0) {
		ans = (n/2)*(n/2);
	} else {
		ans = (n/2)*(n/2+1);
	}

	printf("%d\n", ans);

	return 0;
}