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: Accepted)

/*
This code By @1353055672(Ligen)
[Warning]You're not excepted to understand this code!
RP++
*/
#pragma GCC optimize(3)
#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<queue>
#include<map>
#define ll long long
#define ull unsigned long long
#define mn 5000020
#define mod (int)(1e9+7)
#define FOR(a,b,c) for (register ll a=b;a<=c;a++)
#define FORD(a,b,c) for (register ll a=b;a>=c;a--)
using namespace std;
inline ll read(){
    ll x=0,f=1;
    char c=getchar();
    while (c<'0'||c>'9'){
        if (c=='-')f=-1;
        c=getchar();
    }
    while (c>='0'&&c<='9'){
        x=x*10+c-'0';
        c=getchar();
    }
    return x*f;
}
inline ll Max(ll a,ll b){return (a>b)?a:b;}
inline ll Min(ll a,ll b){return (a<b)?a:b;}
inline ll Abs(ll x){return (x<0)?-x:x;}

int main(){
	ll n=read(),k=read(),ans=(k%2==0)?pow(n/k,3)+pow((n+(k/2))/k,3):pow(n/k,3);
	printf("%lld\n",ans);
	return 0;
}