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 Python (3.4.3) (judge verdict: Runtime Error)

n,k=map(int, input().split())
if k%2==0:
    x=0
    y=0
    for i in range(1,n+1):
        if i%k==k//2:
            x+=1
        if i%k==0:
            y+=1
    ans=0
    if x>=1:
        ans+=com(x,1)
    if x>=2:
        ans+=6*com(x,2)
    if x>=3:
        ans+=6*com(x,3)
    if y>=1:
        ans+=com(y,1)
    if y>=2:
        ans+=6*com(y,2)
    if y>=3:
        ans+=6*com(y,3)
    print(ans)
else:
    x=0
    for i in range(1,n+1):
        if i%k==0:
            x+=1
    ans=0
    if x>=1:
        ans+=com(x,1)
    if x>=2:
        ans+=6*com(x,2)
    if x>=3:
        ans+=6*com(x,3)
    print(ans)
    
def com(a,b):
    r=1
    for i in range(b):
        r*=(a-i)
        r//=i+1
    return r