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>
#define rep(i,n) for(int (i) = 0;(i) < (n);(i)++)
#define SORT(c) sort((c).begin(),(c).end())
#define MOD 1000000007 //S(vector).size()
using namespace std;
typedef long long ll;

int main(void){
  int n, k;
  cin >> n >> k;

  ll cnt = 0;
  if(k % 2 == 1){
    int tmp1 = n / k;
    cout << tmp1 * tmp1 * tmp1 << endl;
  }
  else {
    int tmp2 = n / k;
    cnt += tmp2 * tmp2 * tmp2;
    int tmp3 = 2 * n / k - tmp2;
    cnt += tmp3 * tmp3 * tmp3;
    cout << cnt << endl;
  }
  return 0;
}