A pile of steel pipes is stacked into a trapezoidal cross section. There are 12 steel pipes in the uppermost layer and 28 steel pipes in the lowermost layer. The difference between two adjacent layers is 1 steel pipe. How many steel pipes are there in this pile?
一堆钢管堆成截面为梯形的形状，最上层有12根，最下层有28根，每相邻的两层相差1根，这堆钢管共有多少根．
<gadget id="calculator">12 + 28</gadget>
<output>40</output>

<gadget id="calculator">28 - 12</gadget>
<output>16</output>

<gadget id="calculator">16 + 1</gadget>
<output>17</output>

<gadget id="calculator">17 / 2</gadget>
<output>17/2 = around 8.5</output>

<gadget id="calculator">40 * (17/2)</gadget>
<output>340</output>

<result>340</result>