The Great Escapade

Mr. Krabs loves money. He enters a bank and sees that there are n rooms arranged in a row. The only rooms with doors are the two rooms on either corner. Initially, all the rooms are locked (including the corner ones). To enter a room, it must be unlocked with a key. Mr. Krabs is able to steal k keys from the sleeping night guard. Each key can be used to unlock only one room. To reach one of the i