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 <string>
#include <numeric>
#include <vector>
#include <queue>
#define rep(i,n) for(int i=0;i<n;i++)
#define ll long long int
#define ii pair<int,int>
#define MAX 1000000007

using namespace std;

int main(void){
	int n,k;

	cin>>n>>k;
	if(k%2==1){
		int num=n/k;
		cout<<num*num*num<<endl;
	}
	else{
		int num=n/k;
		int num2=(n-k/2)/k+1;
		if(n<k/2)num2=0;
		cout<<num*num*num+num2*num2*num2<<endl;
	}

	return 0;

}