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 Lua (5.3.2) (judge verdict: Accepted)

N=io.read("n")
K=io.read("n")
if K%2==1 then
  s=0
  for i=K,N,K do
    s=s+1
  end
  s=s*s*s
end
if K%2==0 then
  s=0
  for i=K//2,N,K//2 do
    s=s+1
  end
  if s%2==0 then
    s=s*s*s//4
  else
    s=math.ceil((s//2)^3+(s//2+1)^3)
  end
end
print(s)