A book has 50 pages, number the pages 1, 2, 3, 4, ..., and ask how many times the number 1 appears in the page number.
一本书有50页，编上页码1、2、3、4、…，问数字1在页码中出现多少次．
<gadget id="calculator">1 * 3</gadget>
<output>3</output>

<gadget id="calculator">1 + 11 + 3</gadget>
<output>15</output>

<result>15</result>