A book has 500 pages, number the pages 1, 2, 3... and ask how many times the number 1 appears in total.
一本书有500页，分别编上1，2，3…的页码，问数字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>