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,x;
    long long z = 0,an = 0;

    scanf("%d %d",&n,&k);

    if( n > k ){
        for(x=1;n >= k*x;x++) z++;
        an += z*z*z;
        z = 0;
    }
    if( k%2 == 0 ){
        for(x=0;n >= k/2+k*x;x++) z++;
        an += z*z*z;

    }

    printf("%d\n",an);

    return 0;

}