A story book has 29 pages, so what is the middle page?
一本故事书共29页，那么最中间的一页是第多少页．
<gadget id="calculator">29 - 1</gadget>
<output>28</output>

<gadget id="calculator">28 / 2</gadget>
<output>14</output>

<gadget id="calculator">14 + 1</gadget>
<output>15</output>

<result>15</result>