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)

/*******************************
 * written by Koki Riho
 * Rih0z https://github.com/Rih0z
 *******************************/

#include<iostream>
#include<map>
#include<vector>
#include<string>
#include<numeric>
#include<algorithm>

#define DEBUG false

#define FOR(i , a, b) for(size_t i = a ; i < b ; i++ )
#define REP(i,b) FOR(i , 0 , b)
#define RFOR(i,a,b) for(size_t i = a-1 ; i >= b ; i--)
#define RREP(i,a) RFOR(i,a,0)



typedef long long ll;
using namespace std;

int scanInt(void);
string scanString(void);

void scanLlArr(ll *a , int n);
void scanCharArr(char *string);

void printInt(int p);
void printLlArr(ll *a);
void printCharArr(char *string);


void perSum(ll *a , ll *sum ,int n);

/*************Global variable  **************/
int N ;
int K ;
char str[26];
std::map<char,int> M ;
/*******************************/

int main(){
  if (DEBUG){
    std::printf("******debug mode********\n");
  }
  cin >> N >> K ;
  ll a  = 0 ;
  ll b  = 0 ;
  for (int x = 1 ; x <= N ;  x++){
  if( x%K == 0 )
    a++;
  if( x%K ==K/2 )
    b++;
  }
  ll ans = 0 ;
  ans += a*a*a;
  ans += b*b*b ;
  cout << ans << endl ;



  if (DEBUG){
    std::printf("******debug********\n");

    std::printf("******debug********\n");
  }
  return 0 ;
}

//各地点までの部分和を計算する
void perSum(ll *a , ll *sum ,int n){
  int i ;
  sum[0] = a[0];
  for(i = 1 ; i < n ; i++){
    sum[i] = a[i] + sum[i-1];
  }

}