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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <math.h>

int fact(int n);

int main()
{
	int i, j, n, k, cnt, ans = 0; 
	
	scanf("%d %d", &n, &k);		
	
	if(k % 2 == 0){
		cnt = 0;
		for(i = k / 2; i <= n; i += k){
			cnt++;
		}
		if(cnt >= 1){
			ans += (int)pow((double)cnt, (double)3);
		}
	}
	
	cnt = n / k;
	if(cnt >= 1){
		ans += (int)pow((double)cnt, (double)3);
	}
	
	printf("%d", ans);


	return 0;
}