There is a steel pipe with a ring-shaped bottom. The diameter of the outer circle is 40 cm, and the diameter of the inner circle is 20 cm. The length of this steel pipe is 250 cm. What is the volume of this steel pipe in cubic centimeters?
有一段底面是环形的钢管，外圆直径是40厘米，内圆直径是20厘米，这根钢管长250厘米，求这根钢管的体积是多少立方厘米？
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 ** 2</gadget>
<output>400</output>

<gadget id="calculator">3.14 * 400 * 250</gadget>
<output>314_000</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100 * 250</gadget>
<output>78_500</output>

<gadget id="calculator">314_000 - 78_500</gadget>
<output>235_500</output>

<result>235_500</result>