There are 500 pages in a book, and the page numbers are 1, 2, 3, 4...499, 500. How many times does the number "2" appear in the page number?
一本书共有500页，编上页码1、2、3、4…499、500，数字"2"在页码中一共出现了多少次．
<gadget id="calculator">3 * 20</gadget>
<output>60</output>

<gadget id="calculator">20 + 120 + 60</gadget>
<output>200</output>

<result>200</result>