A pile of logs has an isosceles trapezoid in cross-section. It is known that there are 12 logs in the top layer and 20 logs in the bottom layer, and the bottom layer has 1 more than the top layer. How many logs are there in total in this pile?
一堆圆木，它的横截面形状成等腰梯形．已知圆木最上面一层有12根，最下面的一层有20根，并且下面一层都比上面一层多1根．求这堆圆木共有多少根？
<gadget id="calculator">12 + 20</gadget>
<output>32</output>

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

<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">32 * (9/2)</gadget>
<output>144</output>

<result>144</result>