A pile of utility poles has 5 layers. There are 8 poles on the first level, and one more than the upper level on each lower level. How many utility poles are there in total?
一堆电线杆，共有5层，第一层有8根，下面每层比上层多一根，这堆电线杆一共有多少根？
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">8 + 4</gadget>
<output>12</output>

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

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">20 * (5/2)</gadget>
<output>50</output>

<result>50</result>