Problem:
Score : 300 points

Problem Statement

You are given integers N and K. Find the number of triples (a,b,c) of positive integers not greater than N such that a+b,b+c and c+a are all multiples of K.
The order of a,b,c does matter, and some of them can be the same.

Constraints

1 \leq N,K \leq 2\times 10^5

N and K are integers.

Input

Input is given from Standard Input in the following format:

N K

Output

Print the number of triples (a,b,c) of positive integers not greater than N such that a+b,b+c and c+a are all multiples of K.

Sample Input 1

3 2

Sample Output 1

9

(1,1,1),(1,1,3),(1,3,1),(1,3,3),(2,2,2),(3,1,1),(3,1,3),(3,3,1) and (3,3,3) satisfy the condition.

Sample Input 2

5 3

Sample Output 2

1

Sample Input 3

31415 9265

Sample Output 3

27

Sample Input 4

35897 932

Sample Output 4

114191

Solution in C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>

int main(){
        int a, b, c;
        int n, k;

        int s = 0;

        scanf("%d %d", &n, &k);

        if(k%2 == 1) s = (n/k)*(n/k)*(n/k);
        else if(k%2 == 0){
                int t = n/(k/2);
                for(a = 0; a < t; a++){
                        for(b = 0; b < t; b++){
                                for(c = 0; c < t; c++){
                                        if((a+b)%2==0 && (b+c)%2==0 && (c+a)%2==0) s++;

                                }
                        }
                }
        }

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

        return 0;
}