There are two layers of books on the bookshelf. There are 208 books on the first layer and 124 books on the second layer. Take 2 books from the first layer and put them into the second layer each time. After taking several times, the number of books on the two floors is equal?
书架上有两层图书，第一层有图书208本，第二层有124本，每次从第一层拿2本放入第二层．拿几次后，两层图书的本数相等？
<gadget id="calculator">208 + 124</gadget>
<output>332</output>

<gadget id="calculator">332 / 2</gadget>
<output>166</output>

<gadget id="calculator">208 - 166</gadget>
<output>42</output>

<gadget id="calculator">42 / 2</gadget>
<output>21</output>

<result>21</result>