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<bits/stdc++.h>
using namespace std;

#define ED return 0;
#define UP(a,b) ((a+(b-1))/b)
#define SORT(vec) sort(vec.begin(),vec.end());
#define DOUBLECHANGE(count) cout << setprecision(count);
#define REV(vec) reverse(vec.begin(),vec.end());
#define ipow(x,y) long(pow(x,y))
const long long mod = 1000000007;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    long long int N, K;
    cin >> N >> K;
    long long int answer = 0;
    if(N < K){
        if(N*2 < K){
            cout << 0 << endl;
        }
        else{
            cout << 1 << endl;
        }
        ED
    }
    for(long long int i = 0;i < K;i++){
        if(3 * i % K == i){
            long long int a;
            a = (N-i)/K+1;
            if(i == 0){
                a--;
            }
            answer += pow(a,3);
        }
    }
    cout << answer << endl;
}