Use a fence to surround a square fence with a side length of 50 meters against one wall. How long should the fence be?
靠一面墙用篱笆围一个边长50米的正方形篱笆，篱笆要用多长？
<gadget id="calculator">50 * 3</gadget>
<output>150</output>

<result>150</result>