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: Accepted)

#include<iostream>
typedef long long ll;

using namespace std;

int main()
{ll N, K;
 cin >> N >> K;
  if(K%2 != 0){cout << (long long) (N/K)*(N/K)*(N/K) << endl;}
 else
 {ll cnt1 =  (N/K)*(N/K)*(N/K);
  ll cnt2 = ((N + (K/2))/K)*((N + (K/2))/K)*((N + (K/2))/K);
  cout << cnt1 + cnt2 << endl;
 }
 return 0;}