There are 400 science and technology books in the library, which are less than story books (1/5). How many story books are there?
图书馆有科技书400本，比故事书少(1/5)，故事书有多少本？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">400 / (4/5)</gadget>
<output>500</output>

<result>500</result>