Mom bought a square tablecloth with a side length of 10 decimeters. Now I want to sew a circle of lace on this tablecloth. How long should I prepare for the lace?
妈妈买回来一块方形的桌布，边长是10分米，现在要给这块桌布缝上一圈花边，请问要准备多长的花边？
<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<result>40</result>