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;
#define ll long long
#define pb push_back
#define all(x) x.begin(),x.end()
#define pll  pair <long long,long long>
#define ss second
#define ff first
#define inf 9223372036854775807
#define maa 1000000007
#define ld long double
#define fast  ios_base::sync_with_stdio(false);cin.tie(NULL);
#define bug(x) cout << #x <<": " << x << '\n';
const ll N=3501 ;
int main()
{
   fast ;
   ll n,k ;
   cin>>n>>k ;
   ll ans=0 ;
   for(ll a=0;a<k;a++)
   {
       ll x=(n-a)/k ;
       if(x>=0)
       {
           ll b=k-a ;
           b%=k ;

           ll y=(n-b)/k ;
           if(y>=0)
           {
               if((b+b)%k==0)
               {
                   if(a!=0)
                   ans+=(x+1)*(y+1)*(y+1) ;
                   else
                    ans+=x*y*y ;

               }
           }
       }
   }
   cout<<ans ;

}