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<vector>
#include<algorithm>
#include<cmath>
#include<set>

using namespace std;
using ll = long long;


int main() {
    int n,k,num,ans=1;
    cin >> n >> k;
    if(k%2==1){
        int num=n/k;
        ans = num*num*num;
    }
    else{
        int cnt1=0,cnt2=0;
        for(int i=1;i<=n;i++){
            if(i%k==(k/2))  cnt1++;
            else if(i%k==0) cnt2++;
        }
        ans = cnt1*cnt1*cnt1+cnt2*cnt2*cnt2;
    }
    cout << ans << endl;
	return 0;
}