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 <stdio.h>
#include <string.h>
#include <vector>
#include <numeric>
#include <algorithm>
#include <functional>
#include <math.h>

using namespace std;

typedef vector<int> vi;
typedef pair<int, int> pii;

int main() {
  long long n, k;
  scanf("%lld %lld", &n, &k);

  long long p = n / k;
  long long ans = p * p * p;

  if (k == 2) {
    long long p2 = (n + 1) / k;
    ans += (p2 * p2 * p2);

    printf("%lld", ans);

    return 0;
  }
  

  
  if (k % 2 == 0) {
    ans += (p + 1) * (p + 1) * (p + 1);
  }


  printf("%lld", ans);


  return 0;
}