This is a somewhat evil restaurant. When it has available seats, customers can have seats immediately and stay as long as they want. When the restaurant is full, customers need to wait on a queue. The strange thing is that new customers are led to the head of the queue. If you are the first customer who starts a queue, be prepared to wait for a long time because new customers join in front of you. And the waiter will tell you to leave the queue because you waited too long (timeout) or a new customer is joining the queue but the queue is too long (stack full)!