Teacher Wang distributed some exercise books to the students. The average distribution to 18 students was less than 3 books, and the average distribution to 27 students was also less than 3 books. What is the minimum number of these exercise books?
王老师把一些练习本分给同学们，平均分给18人少3本，平均分给27人也少3本，这些练习本至少多少本．
<gadget id="calculator">3 * 3 * 2 * 3</gadget>
<output>54</output>

<gadget id="calculator">54 - 3</gadget>
<output>51</output>

<result>51</result>