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<bits/stdc++.h>
using namespace std;
int L,s,tot=0,n;
struct edge 
{
	int x,y,v;
}a[100];
int main()
{
	s=1,n=1;
	scanf("%d",&L);
	L--;
	while (L>s&&n<20)
	  {
	  	L-=s;
	  	a[++tot].x=n;a[tot].y=++n;a[tot].v=s;
	  	a[++tot].x=n-1;a[tot].y=n;a[tot].v=0;
	  	s*=2;
	  }
	if (n==20)
	  {
	    if (L>(s>>1))
	    for(int i=1;i<n;++i)
	      {
	        a[++tot].x=i;a[tot].y=i+1;a[tot].v=L-(s>>1)+(1<<(i-1));
	      }
	  }
	else 
	if (L)
	  {
	    a[++tot].x=n;a[tot].y=++n;a[tot].v=L;
	    a[++tot].x=n-1;a[tot].y=n;a[tot].v=0;
	  }
	printf("%d %d\n",n,tot);
	for(int i=1;i<=tot;++i)
	  printf("%d %d %d\n",a[i].x,a[i].y,a[i].v);
	return 0;
}