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>

main ()

{
    int a,n,c,cc;
    scanf ("%d",&a);
    n=a/2;
    if (a%2==1)
    {
        c=n*(n+1);
        printf ("%d",c);
    }
    else if (a%2==0)
    {
        cc=n*n;
        printf ("%d",cc);
    }
    return 0;
}