If the radius of a circle increases from 2 cm to 3 cm, how much does the circumference increase in cm?
一个圆的半径由2厘米增加到3厘米，周长增加了多少厘米．
<gadget id="calculator">3 - 2</gadget>
<output>1</output>

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

<result>6.28</result>