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: Time Limit Exceeded)

#include<bits/stdc++.h>
using namespace std;
int main(){
  int n,k;cin>>n>>k;
  int sum=0;
  for(int a=1;a<=n;a++){
    for(int b=a;b<=n;b++){
      if((a+b)%k==0&&(b-a)%k==0)
        for(int c=b;c<=n;c++){
          if((c-a)%k==0&&(c-b)%k==0&&2*c%k==0){
            if(a<b&&b<c)
              sum+=6;
            else if((a==b&&b<c) || (a<b&&b==c))
              sum+=3;
            else 
              sum++;
          }
        }
    }
  }
  cout<<sum<<endl;
}