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 (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func main() {
	var scanner = bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)

	var n, k int
	if scanner.Scan() {
		tmp := scanner.Text()
		n, _ = strconv.Atoi(tmp)
	}
	if scanner.Scan() {
		tmp := scanner.Text()
		k, _ = strconv.Atoi(tmp)
	}

	if k%2 == 0 {
		var rs1, rs2 []int
		for i := 1; i <= n; i++ {
			if i%k == 0 {
				rs1 = append(rs1, i)
			} else if i%k == k/2 {
				rs2 = append(rs2, i)
			}
		}
		fmt.Println(len(rs1)*len(rs1)*len(rs1) + len(rs2)*len(rs2)*len(rs2))
	} else {
		var rs []int
		for i := 1; i <= n; i++ {
			if i%k == 0 {
				rs = append(rs, i)
			}
		}
		fmt.Println(len(rs) * len(rs) * len(rs))
	}
}