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 Pascal (FPC 2.6.2) (judge verdict: Wrong Answer)

var
	a,b,c:longint;
	n,k,s:int64;
function ans(x:longint):int64;
begin
	if x mod k=0 then exit(n div k)
	else exit(n div k+1);
end;
begin
	read(n,k);
	s:=0;
	for a:=1 to n do
		if (a mod k=0) or (k mod 2=0) and (a mod k=k div 2) then
			s:=s+ans(a)*ans(k-a);
	writeln(s);
end.