There are 8 logs in the top layer of a pile of logs, and 20 logs in the bottom layer. There is a difference of 1 log in every two adjacent layers. How many logs are there in total in this pile?
一堆圆木的最上层是8根，最下层是20根，每相邻两层相差1根，这堆圆木共有多少根．
<gadget id="calculator">8 + 20</gadget>
<output>28</output>

<gadget id="calculator">20 - 8</gadget>
<output>12</output>

<gadget id="calculator">12 + 1</gadget>
<output>13</output>

<gadget id="calculator">13 / 2</gadget>
<output>13/2 = around 6.5</output>

<gadget id="calculator">28 * (13/2)</gadget>
<output>182</output>

<result>182</result>