circle is surrounded by an iron wire, and its radius is exactly 4 decimeters. If this iron wire is used to form a square, what is the length of its side?
用一根铁丝围成一个圆，半径正好是4分米，如果用这根铁丝改围成一个正方形，它的边长是多少分米．
<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>