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>
#include<iomanip>
#include <algorithm>
#include <vector>
#include <string>
#include <utility>
#include <queue>
#define INF 1e9+7
#define rep(i,m,n) for(int i=m;i<n;i++)
#define mrep(i,m,n) for(int i=m;i>n;i--)
#define NO cout<<"NO"<<endl;
#define YES cout << "YES"<<endl;
#define No cout << "No"<<endl;
#define Yes cout << "Yes"<<endl;
#define all(a) a.begin(),a.end()
using namespace std;
typedef long long int ll;
typedef unsigned long long int ull;


//(int)'a'は97 (int)'A'は65 (int)'1'は49
//おまじない

int main() {

	ll n, k;
	ll ans = 0;
	ll a = 0, b = 0;
	cin >> n >> k;

	if (k % 2 == 0) {
		for (int i = 1; i<= n; i++) {
			if (i%k == k / 2) {
				a++;
			}
			else if (i%k == 0) {
				b++;
			}
		}
		ans = a * a*a + b * b*b;
	}
	else {
		for (int i = 1; i <= n; i++) {
			if (i%k == 0) {
				ans++;
			}
		}
		ans = ans * ans*ans;
	}

	cout << ans << endl;

	return 0;
}