A square is surrounded by a piece of iron wire, and the side length is exactly 6.28 meters. If it forms a circle, what is the radius of the circle?
用一根铁丝围成一个正方形，边长正好是6.28米．如果围成一个圆，这个圆的半径是多少？
<gadget id="calculator">6.28 * 4</gadget>
<output>25.12</output>

<gadget id="calculator">25.12 / 3.14 / 2</gadget>
<output>4</output>

<result>4</result>