Class 31 borrowed 29 books, Class 32 borrowed 32 books, and Class 33 borrowed 24 books less than the total borrowed by Class 1 and Class 2? (First ask a problem that uses two-step calculations, and then calculate.)
三1班借书29本，三2班借32本，三3班借的书比一班和二班借的总数少24本，？(先提一个用两步计算的问题，然后再计算．)
<result>3</result>