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 9.2.1) (judge verdict: Accepted)

 #include<stdio.h>
 int main(void)
 {
     int K;
     int i,j=0,k=0;

     scanf("%d",&K);

     for(i=1;i<=K;i++){
       if(i*2<=K) j++;
       else break;
     }

     for(i=0;i<=K;i++){
       if(i*2+1<=K) k++;
       else break;
     }

     printf("%d\n",j*k);

     return 0;
 }