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 x1,y1,x2,y2;
scanf("%d%d%d%d",&x1,&y1,&x2,&y2);

int x3,y3,x4,y4;

if((x1!=x2)&&(y1==y2)){
x3=x2; y3=(x2-x1)+y2;   x4=x1;  y4=y1+(x2-x1);
}
else
if((x1==x2)&&(y1!=y2))
{x3=(y1-y2)+x2; y3=y2; x4=(y1-y2)+x1;    y4=y1;}

printf("%d %d %d %d\n",x3,y3,x4,y4);


return 0;
}