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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>
#include <set>
#include <tuple>

int main()
{
    int N, K;
    std::cin >> N >> K;
    std::set<std::tuple<int, int, int>> ans;
    for (int i = 1; i < N; i++) {
        for (int j = 1; j < N; j++) {
            for (int k = 1; k < N; k++) {
                if ( (i+j)%K==0 && (i+k)%K==0 && (j+k)%K == 0 ) {
                    ans.insert(std::make_tuple(i, j, k));
                }
            }
        }
    }

    std::cout << ans.size() << std::endl;

    return 0;
}