If the lengths of the three sides of a triangle are all even numbers, and the lengths of the two sides are 2 cm and 8 cm respectively, what is its perimeter?
一个三角形的三边长都为偶数，其中两边的长分别为2cm和8cm，则它的周长为多少．
<gadget id="calculator">2 + 8 + 8</gadget>
<output>18</output>

<result>18</result>