A has a number of books, B borrows half and adds 1 book, C borrows half of the remaining books and adds 2 books, and D borrows half of the remaining books and adds 3 books, and finally A still has 2 books, ask A why How many books are there?
A有若干本书，B借走一半加1本，剩下的书C借走一半加2本，再剩下的书D借走一半加3本，最后A还有2本书，问A原有多少本书？
<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">2 * 5</gadget>
<output>10</output>

<gadget id="calculator">10 + 2</gadget>
<output>12</output>

<gadget id="calculator">2 * 12</gadget>
<output>24</output>

<gadget id="calculator">24 + 1</gadget>
<output>25</output>

<gadget id="calculator">2 * 25</gadget>
<output>50</output>

<result>50</result>