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 a,i,j,k,b=0;
    scanf("%d",&a);
    for(i=2;i<=a;i++)
    {
        if(i%2!=0)
        {
            for(j=i+1;j<=a;j=j+2)
                b++;
        }
        else
        {
            for(j=i;j<=a;j=j+2)
                b++;
        }
    }
    printf("%d\n",b);


    return 0;
}