I am an IMG from Europe. All I used to study was First Aid CS. I studied by myself for a month and a half. I read the book 4 times. The 5th time all I read was the Differential Diagnosis, Diagnostic Workup, and that was 2 days before the exam. Remember: First Aid for Step 1 and Step 2 CS. Master the Boards for Step 2 CK and for Step 3. Good Luck!