A cylindrical oil barrel has a diameter of 40 cm at the bottom and a height of 50 cm when measured from the inside. What is its volume in liters?
一个圆柱形油桶，从里面量底面直径是40厘米，高是50厘米，它的容积是多少升？
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

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

<gadget id="calculator">50 / 1_000</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">3.14 * 400 * (1/20)</gadget>
<output>62.8</output>

<result>62.8</result>