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 <map>
#include <algorithm>
#include <cstdlib>
#include <cmath>
#include <numeric>
#include <tuple>
#include <stack>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define print(s) cout << s << endl
using namespace std;
const int INF = 1e9;
typedef long long lint;
const lint LINF = 1e18;
const lint MOD = 1e9 + 7;
// const lint MOD = 998244353;
int ctoi(char c) {
	if (c >= '0' && c <= '9') {
		return c - '0';
	}
	return 0;
}
char upper(char c){
	return c-0x20;
}
char lower(char c){
	return c+0x20;
}

int gcd(int x, int y) {
  if (y == 0) return x;
  return gcd(y, x%y);
}
 
int main(){
	int n,k; cin>>n>>k;
	int ans = 0;
	ans += pow(n/k,3);
	if (k%2==0){
		ans += pow(n/(k/2) - n/k,3);
	}
	cout << ans << endl;
}