The length and width are respectively 6.28 decimeters and 4 decimeters. A rectangular iron sheet is added to maintain a small cylindrical tube after adding a bottom surface. What is the maximum volume of this small tube?
长，宽分别是6.28分米，4分米的长方形铁片，另加一个底面后把它维持一个圆柱形小筒，这个小筒的最大容积是多少？
<gadget id="calculator">6.28 / 3.14 / 2</gadget>
<output>1</output>

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

<gadget id="calculator">3.14 * 1 * 4</gadget>
<output>12.56</output>

<result>12.56</result>