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 N,K;
    int i, j, k;
    int tmp1, tmp2;

    scanf("%d %d", &N, &K);

    if(K%2 == 1){
        tmp1 = N/K;
        printf("%d", tmp1*tmp1*tmp1);
    }else{
        tmp1 = N/K;
        tmp2 = (N+K/2)/K;
        tmp1 = tmp1*tmp1*tmp1;
        tmp2 = tmp2*tmp2*tmp2;
        printf("%d", tmp1+tmp2);
    }

    return 0;
}