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: Accepted)

def solve(N,K):
    #方針
    #a mod K == a'(a' != 0)のとき
    #b mod K == c mod K == -a'
    #(b+c) mod K == -2a'
    #これで上手くいく(-2a' mod K == 0)のはKが偶数のときのみ
    if K % 2 != 0:
        return (N // K) ** 3
    else:
        return (N // K) ** 3 + ((N + K // 2) // K) ** 3

def main():
    N,K = map(int,input().split())

    print(solve(N,K))

if __name__ == "__main__":
    main()