A square is surrounded by a piece of iron wire, and its side length is 15.7 cm. If it is used to form a circle, what is the diameter of the circle in cm?
用一根铁丝围成一个正方形，它的边长为15.7厘米，如果用它围成一个圆这个圆的直径为多少厘米？
<gadget id="calculator">4 / 3.14</gadget>
<output>1.273885</output>

<gadget id="calculator">15.7 * 1.273885</gadget>
<output>19.999994</output>

<result>19.999994</result>