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 C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include "iostream"
#include "algorithm"
#include "vector"
#include "string"


int main(int argc, char const *argv[]) {

  // std::string A;
  // std::cin >> A;
  // std::cout << A[0] << '\n';
  //
  // int NN;
  // std::cin >> NN;
  // std::cout << NN*NN << '\n';

  int NN, KK;

  std::cin >> NN>>KK;

  long long ans = 0;

  for (size_t a = 1; a < NN + 1; a++) {
    int b = KK - a % KK;
    if ((2*b )% KK == 0) {
      int kosu = (NN-b) / KK + 1;
      ans+= kosu * kosu;
    }
  }

  std::cout << ans << '\n';

  return 0;
}