Wang Yaozu has a 12-page book, starting from the beginning, with a leaf inserted every 3 pages, how many leaves are put in this book?
王耀祖有一本12页的书，从头开始，每隔3页夹一片树叶，这个本子一共放进了多少片树叶？
<gadget id="calculator">12 / 3</gadget>
<output>4</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<result>3</result>