A book has read 390 pages in the first week, and there is still (1/3) of the book left unread. How many pages are there in this book?
一本书第一周读了390页，还剩下这本书的(1/3)没读．这本书共多少页．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">390 / (2/3)</gadget>
<output>585</output>

<result>585</result>