Problem 524/C Codeforces: The art of dealing with ATM

I was trying to solve this problem of codeforces and i ended up very frustrated. I have a solution, and when i try it on the online judge he says me that it didn't work. I have seen it several times in order to find the problem but i definitely can't found it. The strategy is the following:

For each cash withdrawal (from the big one to the little):

• Calculate the number of bills needed for the actual bill denomination. And keep on doing this with the for-bucle.
• If a denomination was used then increase in one the counter.
• Calculate the rest of money using the "module".

Finally, i check the conditions of the problem using a if. The conditions are: not using more than k bills, withdrawal all the mone and don't use more than 2 different denominations.

This is the link for the problem statement and here is my code in C++11.

Link: http://codeforces.com/problemset/problem/524/C

    #include <iostream>

using namespace std;

int main(){
  long long sol,counter;
  int q,n,k;
  cin >> n;
  cin >> k;
  long long a[n]; // types of denominations
  for(int i = 0; i < n; i++){
    cin >> a[i];
  }
  cin >> q;
  long long b[q]; // cash to withdrawal
  for(int i = 0; i < q; i++){
    cin >> b[i];
    sol = 0;
    counter = 0;
    for(int j = n-1; j >= 0; j--){
      sol += b[i]/a[j];
      counter += (b[i]/a[j]!=0);
      b[i] = b[i]%a[j];
    }
    if(sol <= k && b[i] == 0 && counter <= 2){
      cout << sol << endl;
    } else {
      cout << -1 << endl;
    }
  }
}

PD: I am not a native english speaking so sorry if something can't be understood. PD2: I am also begining with C++11 and this kind of problems.

Very thank for your help. I am waiting for some response.