The circumference of the bottom of a cylindrical oil barrel is 12.56dm, and the height is 5dm. If 80% of the full barrel is poured out, how many liters are left?
一个圆柱形油桶底面周长是12.56dm，高5dm，把满桶油倒出80%，还余下多少升？
<gadget id="calculator">12.56 / 3.14 / 2</gadget>
<output>2</output>

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

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3.14 * 4 * 5 * (1/5)</gadget>
<output>12.56</output>

<result>12.56</result>