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 argc, char *argv[])
{
  int N, K;
  scanf("%d%d", &N, &K);
  
  if(K % 2 == 1){
    int ans0 = (N / K) * (N / K) * (N / K);
    printf("%d\n", ans0);
  }
  else{
    int a, b;
    a = N / (K / 2);
    if(a % 2 == 0){
      int ans1 = 2 * (N / K) * (N / K) * (N / K);
      printf("%d\n", ans1);
    }
    else{
      int ans2 = (N/K +1) * (N/K + 1) * (N/K + 1) + (N/K) * (N/K) * (N/K);
      printf("%d\n", ans2);
    }
  }
  
  return 0;
}