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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>

int main(){
  int a,b;
  int ans=0;
  int i,j,k;

  scanf("%d", &a);
  scanf("%d", &b);

  /*for(i=1; i < (a+1); i++){
    for(j=1; j < (a+1); j++){
      if((i+j) % a == 0){
        for(k=1; k < (a+1); k++){
          if((i+k) % a == 0){
            if((j+k) % a == 0) s++;
          }
        }
      }
    }
  }*/

  if(b % 2==0){
    if(b/2<a) {
      ans++;
      for(i=b/2; i<a+1; i += b){
        for(j=b/2; j<a+1; j += b){
          for(k=b/2; k<a+1; k += b){
            if(i==j && j==k && k==i) ans++;
            else if(i==j || j==k || k==i) ans += 3;
            else ans += 6;
          }
        }
      }
    }

    if(b<a) {
      ans++;
      for(i=b; i<a+1; i += b){
        for(j=b; j<a+1; j += b){
          for(k=b; k<a+1; k += b){
            if(i==j && j==k && k==i) ans++;
            else if(i==j || j==k || k==i) ans += 3;
            else ans += 6;
          }
        }
      }
    }

  }else{
    if(b<a) {
      ans++;
      for(i=b; i<a+1; i += b){
        for(j=b; j<a+1; j += b){
          for(k=b; k<a+1; k += b){
            if(i==j && j==k && k==i) ans++;
            else if(i==j || j==k || k==i) ans += 3;
            else ans += 6;
          }
        }
      }
    }
  }

  printf("%d\n",ans);

  return 0;
}