A cylindrical water cup has a bottom diameter of 7 cm. In order to prevent hot hands, a circle of rubber is wrapped in the middle. The joint is 2 cm. What is the length of the rubber in cm?
一个圆柱形水杯，它的底面直径是7厘米，为了防止烫手，在中间缠绕了一圈胶皮，接头处是2厘米，胶皮的长度应该是多少厘米．
<gadget id="calculator">3.14 * 7</gadget>
<output>21.98</output>

<gadget id="calculator">21.98 + 2</gadget>
<output>23.98</output>

<result>23.98</result>