A total of 137 books were donated by 7 classes of the fifth grade in a certain school. The number of books donated by each class is different. Among them, the class that donated the most donated at least how many books.
某校五年级7个班共捐赠图书137本，各班捐赠的图书数量各不相同，其中捐得最多的那个班至少捐多少本．
<result>23</result>