public static double vwap(List<Double> l)
  {
    Double top, bottom;
    top = bottom = 0.0;
            
    for (int i = 0, j = 1;i < (l.size() - 1);i+=2, j+=2) {
      Double price = l.get(i);
      Double num = l.get(j);
      
      top += (price * num);
      bottom += num;
    }
    
    return top / bottom;
  }