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)

#include <iostream>
#include <algorithm>
#include <utility>
#include <set>
#include <vector>
#include <map>
#include <queue>
#include <deque>
#include <stack>
#include <string>

using namespace std;

typedef pair<int, int> pi;
typedef vector<int> vi;
typedef vector<pi> vpi;
typedef long long ll;
typedef vector<ll> vl;
typedef pair<ll, ll> pl;
typedef double db;

#define ini(x) int x; cin >> x
#define inl(x) ll x; cin >> x
#define ins(x) string s; cin >> x

#define out(x) cout << x;
#define outb(x) cout << x << ' ';
#define outn(x) cout << x << '\n';

#define mp make_pair
#define fi first
#define se second
#define pb push_back
#define all(x) x.begin(), x.end()

#define forn(i, s, e) for (int i = s; i < e; i++)
#define ford(i, s, e, d) for (int i = s; i < e; i += d)
#define fors(i, n) for (int i = 1; i*i <= n; i++)

int main() {
	ios::sync_with_stdio(false);
	cin.tie(NULL); cout.tie(NULL);
	
	inl(n);inl(k);
	ll fc = 1LL*(n/k), sc = 0;
	if (k % 2 == 0) sc = fc + 1LL*n % 2;
	//outb(fc); outn(sc);
	ll ret = fc*fc*fc + sc*sc*sc;
	outn(ret);
	
	return 0;
}