Alex has four books of different sizes which he wishes to place on a bookshelf. Unfortunately, the bookshelf has a conspicuous hole at one end through which only the smallest book can fall. If he wishes for all his books to stay stationary, in how many ways can he arrange his books?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Alex has four books of different sizes which he wishes to place on a bookshelf. Unfortunately, the bookshelf has a conspicuous hole at one end through which only the smallest book can fall. If he wishes for all his books to stay stationary, in how many ways can he arrange his books?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
18\text{ ways.}
Alex has four books of different sizes which he wishes to place on a bookshelf. Unfortunately, the bookshelf has a conspicuous hole at one end through which only the smallest book can fall. If he wishes for all his books to stay stationary, in how many ways can he arrange his books?
train