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)

// Author: 23forever
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <vector>
#include <queue>
typedef long long LL;
const int MAXN = 200000;
using namespace std;

inline void enableFileIO() {
  freopen("test.in", "r", stdin);
  freopen("test.out", "w", stdout);
}

inline int read() {
  int x = 0, w = 1;
  char c = ' ';

  while (c < '0' || c > '9') {
    c = getchar();
    if (c == '-') w = -1;
  }
  while (c >= '0' && c <= '9') {
    x = (x << 1) + (x << 3) + (c ^ 48);
    c = getchar();
  }

  return x * w;
}

int n, k;

void init() {
  //enableFileIO();
  
  n = read();
  k = read();
}

int main() {
  init();

  LL ans = 1LL * (n / k) * (n / k) * (n / k);
  if (k % 2 == 0) ans += 1LL * (n - k / 2) / k + 1;    
  printf("%lld\n", ans);
  return 0;
}