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 Ruby (2.3.3) (judge verdict: Accepted)

# 奇数はかんたん 偶数ならkで割ってk/2あまるやつと割り切れるやつのそれぞれ組み合わせしたやつを加算
n, k = gets.chomp.split.map(&:to_i)
ans = 0
if k.odd?
  ans = (n/k).floor ** 3
else
  s = 0
  t = 0
  (1..n).each do |x|
    if x % k  == k / 2
      t += 1
    elsif  x % k == 0
      s += 1
    end
  end
  ans = t ** 3 + s ** 3

end
puts ans