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 Go (1.6) (judge verdict: Accepted)

package main

import "fmt"

func main(){
	var N,K,count,count2 int
	fmt.Scan(&N,&K)
	if K%2 == 0{
		for i:=1;i<N+1;i++{
			if i%K == 0{
				count++
			}else if i%K == (K/2){
					count2++
			}
		}
	}else{
		for i:=1;i<N+1;i++{
			if i%K == 0{
				count++
			}
		}
	}
	fmt.Println(count*count*count+count2*count2*count2)
}