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: Accepted)

#include<stdio.h>

long long san(long long a);

int main()
{
    long long n,k,x,y,num1,num2,ans;
    scanf("%lld %lld",&n,&k);
    x=n%k;
    num1=n/k;
    num2=num1;
    if(k/2<=x)num2++;
    if(k==1)printf("%lld",n*n*n);
    else
    {
        if(k%2==0)ans=(san(num1)+san(num2));
        else ans=san(num1);
    printf("%lld",ans);
    }
}
long long san(long long a)
{
    return (a*a*a);
}