A book has 500 pages in total, and the pages are numbered 1, 2, 3, ..., 499, 500. In these page numbers, how many times does the number "1" appear?
一本书共有500页，分别编上页码1、2、3、…、499、500．在这些页码中，数字"1"共出现了多少次．
<gadget id="calculator">100 + 20</gadget>
<output>120</output>

<gadget id="calculator">3 * 20</gadget>
<output>60</output>

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

<result>200</result>