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>
int main() {
	long long int k, n,i,a,b,c,result=0;
	scanf("%lld%lld", &n, &k);

	if (k % 2 == 1) {
		printf("%lld", (n%k)*(n%k)*(n%k));
	}
	else {
		if (n%k >= k / 2) {
			printf("%lld", (n%k)*(n%k)*(n%k)+ (n%k+1)*(n%k+1)*(n%k+1));
		}
		else {
			printf("%lld", 2*(n%k)*(n%k)*(n%k));
		}
	}
	
}