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>
/*
g++ -std=c++11 -Wall -g -fsanitize=undefined -D_GLIBCXX_DEBUG arc/arc102/c.cpp
*/
using namespace std;
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define SZ(x) ((int)(x).size())
#define INF (1e16)
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);//おまじないでcin, cout早くする
    ll N, K;
    cin >> N >> K;
    if(K % 2 == 1){
        cout << pow(N/K, 3) << "\n";
    }else{
        if((N/K) * K + (K/2) > N){
            cout << 2 * pow(N/K, 3) << "\n";
        }else{
            cout << 2 * pow(N/K, 3) + 3 * pow(N/K, 2) + 3 * pow(N/K, 1) + 1 << "\n";
        }
    }
    return 0;
}