A 55-year-old woman comes to OPD complaining of recurrent RUQ pain (especially after heavy meals) radiating to the right shoulder and to the back, associated with nausea but no vomiting. She has hyperbilirubinemia, normal ALT/AST but high ALP and GGT. Abdominal ultrasound shows multiple small gallbladder stones but CBD can not be visualized. Which of the following will be the appropriate next step?