If the radius of a circle increases from 1 decimeter to 2 decimeters, how much does its circumference increase
一个圆的半径由1分米增加到2分米，它的周长增加多少分米
<gadget id="calculator">3.14 * 2 * 2</gadget>
<output>12.56</output>

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

<gadget id="calculator">12.56 - 6.28</gadget>
<output>6.28</output>

<result>6.28</result>