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)

n, k = gets.split.map(&:to_i)
# n = 3
# k = 2
#
# def binom(m, n)
#   res = 1
#   (1..n).each do |i|
#     res = res * (m - i + 1) / i
#   end
#   return res
# end
#
# def multi_choose(m, n)
#   binom(m + n - 1, n)
# end

if (k % 2 == 0)
  # kの倍数の個数
  multiple_k = n / k
  a = multiple_k**3
  # mod kで k/2 になる数の個数
  middle_mod = (n + k/2) / k
  b = middle_mod**3

  puts a + b
else
  # kの倍数の個数
  multiple_k = n / k
  puts multiple_k**3
end