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<stdbool.h>
#include<ctype.h>
#define mprint(x) printf(FORMATCONVERSION(x),(x))
#define FORMATCONVERSION(x) _Generic((x),\
                                    int:"%d",unsigned int:"%u",\
                                    double:"%lf",long long int:"%lld",\
                                    unsigned long long int:"%llu",\
                                    char :"%c",char*:"%s")

#define mswap(x,y) _Generic((x),int:swap_int,unsigned int:swap_uint,\
                            long long:swap_ll,unsigned long long:swap_ull)(&(x),&(y))

void swap_int(int *a,int *b){int tmp = *a;*a = *b;*b= tmp;return;}
void swap_uint(unsigned int *a,unsigned int *b){unsigned int tmp = *a;*a = *b;*b= tmp;return;}
void swap_ll(long long *a,long long *b){long long tmp = *a;*a = *b;*b= tmp;return;}
void swap_ull(unsigned long long *a,unsigned long long *b){unsigned long long tmp = *a;*a = *b;*b= tmp;return;}

int main(void){
    unsigned long long n,k;
    unsigned long long int ans = 0;
    scanf("%llu %llu",&n,&k);
    if(k % 2 != 0){
        //ki
        ans += ((n / k) * (n / k) * (n / k));
    }else{
        ans += ((n / k)*(n / k) * (n / k));
        unsigned long long int tmp = n - (k / 2);
        unsigned long long int hoge  = (tmp / k) + 1;
        ans +=  (hoge * hoge * hoge);
    }
    mprint(ans);
    return 0;
}