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)

def gets; ARGF.gets; end

def mul_num(n, k)
  n / k
end

def main
  n, k = gets.split.map(&:to_i)
  if k.even?
    # kの倍数の個数
    e = mul_num(n, k)

    # 倍数間の真ん中の個数
    o = if k / 2 <= n % k
          e + 1
        else
          e
        end

    # puts e
    # puts o
    puts e**3 + o**3
  else
    e = mul_num(n, k)

    puts e**3
  end
end

if __FILE__ == $0
  main
end