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>
#include <string.h>
#include <math.h>

int main()
{
    int N,K;
    scanf("%d%d",&N,&K);

    long long count=0;

    if( K > N ){
        if( K%2==1 ){
            count = 0;
        }else{
            if( N >= K/2 ){
                count = 1;
            }else{
                count = 0;
            }
        }
        return 0;
    }

    if( K % 2 == 1 ){
        count = (N/K) * (N/K) * (N/K);
    }else{
        if( N % K >= K / 2 ){
            count = ( (N/K) * (N/K) * (N/K) ) + ( ( (N/K) + 1 ) * ( (N/K) + 1 ) * ( (N/K) + 1 ) );
        }else{
            count = ( (N/K) * (N/K) * (N/K) ) * 2;
        }
    }

    printf("%lld\n",count);

    return 0;
}