A circle is surrounded by a wire, and the radius is exactly 4 cm. If this wire is changed into a square, what is the length of its side in cm?
用一根铁丝围成一个圆，半径正好是4厘米，如果把这根铁丝改围成一个正方形，它的边长是多少厘米．
<gadget id="calculator">4 / 4</gadget>
<output>1</output>

<gadget id="calculator">3.14 * 2 * 1</gadget>
<output>6.28</output>

<result>6.28</result>