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,ans=0,tmp1,tmp2,i,j;
  scanf("%d%d",&n,&k);
  tmp1 = k%2==0?(k/2):k;
  for(i=tmp1;i<=n;i+=tmp1){
    j=i;
    ans++;
    tmp2=0;
    while(j-k>=1){
      tmp2+=3;
      j-=k;
    }
    if(tmp2>0)
      ans+=2*tmp2-3;
    j=i;
    tmp2=0;
    while(j+k<=n){
      tmp2+=3;
      j+=k;
    }
    if(tmp2>0)
      ans+=2*tmp2-3;
  }
  printf("%d\n",ans);
  return 0;
}