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 <stdlib.h>
int main(){
  int n,k,i,j,l,count=0;
  scanf("%d%d",&n,&k);
  
  for(i=1;i<n;i++){
    for(j=1;j<=i;j++){
		for(l=1;l<=j;l++){
		if((i+j)%k==0 && (j+l)%k==0 && (l+i)%k==0){
			 if(i==j && j==l){
				count++;
             }else if(i!=j && j!=l && l!=i){
               count+=6;
             }else{
               count+=3;
             }
        }
        }
    }
  }
  
  printf("%d", count);
}