A rectangular vegetable field is 18 meters long and 9 meters wide, with one side against a wall and the other three walls surrounded by bamboo fences. How long is the bamboo fence at least?
一块长方形菜地，长18米，宽9米，一面靠墙其它三面墙围上竹篱笆．竹篱笆至少长多少米？
<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<gadget id="calculator">18 + 18</gadget>
<output>36</output>

<result>36</result>