There are a pile of steel pipes, the top layer has 12 pipes, the bottom layer has 26 pipes, and there is a difference between each adjacent upper and lower layers. How many steel pipes are there in this pile?
有一堆钢管，最上层是12根，最下层是26根，每相邻上下两层之间相差一根，这堆钢管共有多少根．
<gadget id="calculator">12 + 26</gadget>
<output>38</output>

<gadget id="calculator">26 - 12</gadget>
<output>14</output>

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

<gadget id="calculator">15 / 2</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">38 * (15/2)</gadget>
<output>285</output>

<result>285</result>