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: Accepted)

#include <stdio.h>

long long calc_combination_num(long long N, long long K);

int main(void)
{
    long long K;
    long long N;
    long long combination;

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

    combination = calc_combination_num(N, K);
    printf("%llu\n", combination);
   
    return 0;

}

long long calc_combination_num(long long N, long long K)
{
    long long combination;
    long long pattern;

    if(K == 0){
        return 0;
    }

    if(K % 2 == 1){
        pattern = N / K;
        combination = pattern * pattern * pattern;
        return combination;
    }else{
        pattern = (N + K / 2) / K;
        combination = pattern * pattern * pattern;
        pattern = N / K;
        combination += pattern * pattern * pattern;
        return combination;
    }
}