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>
using namespace std;


int main()
{
	int n, k,x,y=0,z=0,a=0;
	cin >> n >> k;
	if (k % 2 == 0) {
		y =- k / 2;
		while (1) {
			if (y + k > n)break;
			y += k;
			z++;
			if (y + k / 2 > n) {
				a += z-1;
			}
			else if (y + k > n) {
				a = z+1;
			}
			

			
			if (y > n)break;
			
		}

	}
	else {
		while (1) {
			y += k;
			if (y > n)break;
			z++;
		}
		
	}
	cout << a * a*a + z * z*z << endl;
    return 0;
}