Uncle Wang wants to use a wall (the wall is 30 meters long) and a fence to build a chicken farm with a length of 20 meters and a width of 15 meters. Please help him calculate how many meters of fence he needs at least?
王大爷想利=用院里的一面墙(墙有30米)和篱笆盖一个长20米，宽15米的养鸡场，请你帮他算算他最少需要篱笆多少米？
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">20 + 30</gadget>
<output>50</output>

<result>50</result>