There is a square surrounded by iron wire, and its side length is 6.28 meters. Now if this iron wire is surrounded by a circle, what is the radius of the circle in meters?
有一个用铁丝围成的正方形，量得它的边长是6.28米，现如果把这根铁丝围成圆形，这个圆的半径是多少米？
<gadget id="calculator">4 / 3.14 / 2</gadget>
<output>0.636943</output>

<gadget id="calculator">6.28 * 0.636943</gadget>
<output>4.000002</output>

<result>4.000002</result>