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)

#pragma GCC diagnostic ignored "-Wunused-result"

#include <stdio.h>

int main(void) {
  unsigned long N,K;
  unsigned long count = 0;
  
  scanf("%lu %lu", &N, &K);

  count += (N/K)*(N/K)*(N/K);
  
  if (K%2 == 0){ // even
    int m = N/(K/2) - N/K; 
    count += m*m*m;
  }
  
  printf("%lu\n",count);
  return 0;

}