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: Time Limit Exceeded)

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
int main()
{
  int n,k,a,b,c,max,i,ans=0;
  scanf("%d %d",&n,&k);
  max = 2*n/k;
  for(a=1;a<=n;n++){
    for(b=a;b<=n;b++){
      for(c=b;c<=n;c++){
        if((a+b)%k==0&&(b+c)%k==0&&(c+a)%k==0){
          if(a==b&&b==c){
            ans++;
          }else{
            if(a==b||b==c||c==a){
              ans += 2;
            }else{
              ans += 3;
            }
          }
        }
      }
    }
  }
  printf("%d",ans);
  return 0;
}