There is a square handkerchief, one side of which is 20 cm long. If you want to inlay a beautiful lace on this handkerchief, how long should you prepare for the lace?
有一块正方形手帕，它的一条边长20厘米，要准备在这块手帕上镶一条漂亮的花边，应该准备多长的花边？
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<result>80</result>