book has a total of 1000 pages, and the first page to the last page 999 are put together continuously to form a large number, that is, 12345678910111213...999, so how many digits is this?
一本书共1000页，把第1页一直到最后的第999页连续放在一起，组成一个很大的数，即12345678910111213…999，那么，这是一个几位数？
<gadget id="calculator">99 - 9</gadget>
<output>90</output>

<gadget id="calculator">90 * 2</gadget>
<output>180</output>

<gadget id="calculator">999 - 99</gadget>
<output>900</output>

<gadget id="calculator">900 * 3</gadget>
<output>2_700</output>

<gadget id="calculator">9 + 180 + 2_700</gadget>
<output>2_889</output>

<result>2_889</result>