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(){
	int N,K,a,c,A,C,x,y,ans=0;
	scanf("%d %d",&N,&K);
	x=N%K,y=N/K;
	for(a=0;a<=K-1&&a<=N;a++){
		c=K-a;
		if(K-a>N) c=N;
		if((2*a)%K==0){
			A=C=0;
			if(0<a&&a<=x) A++;
			if(0<c&&c<=x) C++;
			ans+=(y+A)*(y+A)*(y+C);
		}
	}
	printf("%d",ans);
}