A cylinder with a height of 20 centimeters, if the height increases by one centimeter, its surface area will increase by 12.56 square centimeters. What is the volume of the cylinder in cubic centimeters?
一个高20厘米的圆柱，如果高增加一厘米，它的表面积就增加12.56平方厘米，原来这个圆柱的体积是多少立方厘米？
<gadget id="calculator">12.56 / 1 / 3.14 / 2</gadget>
<output>2</output>

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

<gadget id="calculator">3.14 * 4 * 20</gadget>
<output>251.2</output>

<result>251.2</result>