The lengths of two adjacent sides of a parallelogram are 5cm and 8cm respectively, what is the perimeter of this parallelogram in cm?
平行四边形的相邻两条边长分别为5cm、8cm，这个平行四边形的周长是多少cm．
<gadget id="calculator">5 + 8</gadget>
<output>13</output>

<gadget id="calculator">13 * 2</gadget>
<output>26</output>

<result>26</result>