If one side of a parallelogram is 8 cm long and the adjacent side is 5 cm long, what is its perimeter in cm?
一个平行四边形的一条边长是8厘米，邻边长5厘米，它的周长是多少厘米．
<gadget id="calculator">8 + 5</gadget>
<output>13</output>

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

<result>26</result>