For a book, Xiaohong reads 4 pages on the first day, and then reads 1 more page every day than the previous day. By the 4th day, how many pages have she read in total?
一本书，小红第一天读4页，以后每天都比前一天多读1页，读到第4天，一共读了多少页．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">3 * 1</gadget>
<output>3</output>

<gadget id="calculator">4 + 3</gadget>
<output>7</output>

<gadget id="calculator">4 + 7</gadget>
<output>11</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">11 * 2</gadget>
<output>22</output>

<result>22</result>