If a cylinder with a base diameter of 4 decimeters is cut crosswise into two small cylinders, how much does its surface area increase?
把一个底面直径是4分米的圆柱木料横切后分成两个小圆柱，它的表面积增加了多少．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4 * 2</gadget>
<output>25.12</output>

<result>25.12</result>