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 <bits/stdc++.h>
using namespace std;

//#pragma GCC optimize("O3")
//#pragma GCC target("sse4")

#define FOR(i, a, b) for(int i = (a); i < (b); ++i)
#define RFOR(i, b, a) for(int i = (b) - 1; i >= (a); --i)
#define ITER(it, a) for(__typeof(a.begin()) it = a.begin(); it != a.end(); it++)
#define FILL(a, value) memset(a, value, sizeof(a))

#define SZ(a) (int)((a).size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;

const double PI = acos(-1.0);
const int INF = 1000 * 1000 * 1000 + 7;
const LL LINF = (LL)INF * INF;

int main()
{
	ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	//freopen("In.txt", "r", stdin);
	LL n, k;
	cin >> n >> k;
	if(k & 1)
	{
		cout << (n / k) * (n / k) * (n / k);
		return 0;
	}
	LL cntOdd = 0, cntEven = 0;
	k /= 2;
	FOR(i, 1, n + 1)
	{
		if(i % k == 0)
		{
			if((i / k) & 1)
				cntOdd++;
			else
				cntEven++;
		}
	}
	cout << cntOdd * cntOdd * cntOdd + cntEven * cntEven * cntEven;
	return 0;
}