A book has 100 pages in total, and the printed page numbers are 1, 2, 3, 4, ..., 99, 100, so how many times does the number 1 appear in the page number? (Hint: The number "1" in page number "11" counts as 2 occurrences)
一本书共有100页，编印页码1，2，3，4，…，99，100，那么数字1在页码中一共出现多少次．(提示：页码"11"中数字"1"算出现2次)
<gadget id="calculator">10 + 10 + 1</gadget>
<output>21</output>

<result>21</result>