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>
#define PI 3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679
using namespace std;
const int inf=0x3f3f3f3f;
const long long inf2=(1<<62)-1;
const double eps=1e-6;
int dist(int x,int y,int x2,int y2){
	return (abs)(x-x2)*(y-y2);
}
int main(){
	int n,k;
	cin>>n>>k;
	if(k%2!=0){
		cout<<(long long)(n/k)*(n/k)*(n/k);
	}
	if(k%2==0){
		cout<<(long long)((long long)(n/k)*(n/k)*(n/k)+(long long)((n+k/2)/k)*((n+k/2)/k)*((n+k/2)/k));
	}
	return 0;
}