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<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define min(a,b) a<b?a:b
int main()
{
	int n,k,a,b,c,ans=0;
	scanf("%d%d",&n,&k);
	int max=3*n;
	for(int i=k;i<=max;i+=k)
	{
		int m=min(i-1,n);
		for(int j=m;j>=i/2&&i-j>0;--j)
		{
			a=j;
			b=i-j;
			for(int l=1;l<=b;++l)
			{
				if((a+l)%k==0&&(b+l)%k==0)
				{
					//cout<<a<<b<<l<<endl;
					if(a==b&&a==l) ans++;
					else if(a!=b&&a!=l&&b!=l) ans+=6;
					else ans+=3;
				}
			}
		}
	}
	printf("%d\n",ans);
	return 0;
}