Some pirates found a bottle with a note. The note indicated the name of the island where the treasure was buried and its prefix function. Unfortunately, the island's name had not been preserved completely. Your task is to help the pirates restore the name of the island.
Island's name: BA....OS
Prefix function: 00012000How many letters will you have to guess without a clue, keeping in mind that you can make use of the prefix function to restore some missing letters using the existing ones?