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 <cmath>
using namespace std;


bool judge(int a, int b, int K){
    return ((a + b) % K == 0 && (a - b) % K == 0);
}

int main()
{
    int N, K;
    cin >> N >> K;

    int count = 0;

    int S = N % K;
    for(int a = 1; a <= K; ++a){
        int b = K - (a % K);
        
        while((! judge(a,b,K)) && b <= N){
            b += K;
        }
        
        if(b > N){
            continue;
        } else {
            int L = a % K;
            //cout << a <<" " << (N/K + (S > a)  ) << endl;
            count += (((N - b) / K + 1 ) * ((N + L + K) / K - 1)) * (N/K + (S >= a)  );
        }
    }
    
    cout << count << endl;
    
}