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 rep(X,A,B) for(int X=A;X<=B;X++)
#define tep(X,A,B) for(int X=A;X>=B;X--)
#define LL long long
#define DB double
const int N=400010;
const int M=800010;
const int maxn=200000;
const LL MOD=998244353;
using namespace std;

int n,K;

int GET(int x){
	if(x==0)return n/K;
	if(n%K==0)return n/K;
	if(n%K<x)return n/K;
	else return n/K+1;
}

LL CHK(LL i,LL j){
	if(i==j){
		LL c=GET(i);
		return c+c*(c-1)*3+c*(c-1)*(c-2);
	}
/*	else{
		LL ci=GET(i),cj=GET(j);
		return ci*cj*3+cj*(cj-1)*ci*6;
	}*/
}

LL SOLVE(){
	LL res=0;
	res+=CHK(0,0);
	rep(i,1,K-1){
		if(K-i==i)res+=CHK(i,i);
	}
	return res;
}

int main(){
	scanf("%d%d",&n,&K);
	printf("%lld\n",SOLVE());
	return 0;
}