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Asking 'what book should I get for Internal Medicine?' is almost like asking 'what book should I get to be a doctor?'
You will not only have Internal Medicine from the 3rd year until the end of your education at Semmelweis Medical University, but also as a doctor wherever you end up.
Internal Medicine is more or less everything except Surgery in a hospital.
There are some large 'Bibles', such as Harrison's Principles of Internal Medicine. This is my personal favorite and the one I decided to get.
The practical knowledge (how to approach patients, getting familiarized with symptoms etc.) can only be learned through the practice of medicine, so attend your classes! And there are no books that can give you this knowledge.
You should go to the bookstores in Budapest and look through as many large compendia as possible before deciding. Also, talk to other students and your professors/doctors to see what they suggest. So far, the majority of my professors/doctors have recommended Harrison's Principles of Internal Medicine, but Cecil's Textbook of Medicine was also mentioned.
Doesn't matter what you choose, both compendia are huge and will be enough to fill in the cracks from all your other textbooks (Cardiology, Pulmonology, Neurology etc).
Many students also decided to get a pocket guide to carry to the clinic.
My favorite is the Oxford Pocket Guide . Several recommended the Harrison's Principles of Internal Medicine Pocket version. I've seen it and can recommend this as well, although I don't own it.
As you continue with your clinical subjects, you will end up buying more books that cover Internal Medicine topics, or you will just use your large compendium.
I didn't buy any books for Pulmonology (4th year) or Cardiology (4th year), but instead just used my huge Harrison's.
Other large Internal Medicine books you should consider:
Davidson's Principles and Practice of Medicine

Kumar and Clark: Clinical Medicine
Kumar and Clark was recommended by the tutor at the 1st Department of Internal Medicine. He said "it is simple and gives you a good overview".