A cylindrical steel with a cross-sectional diameter of 20 cm and a length of 2 meters, if the steel weighs 7.8 grams per cubic centimeter, how many kilograms does this piece of steel weigh? (retain two decimal places)
一根横截面直径为20厘米的圆柱形钢材，长2米，如果每立方厘米钢重7.8克，这段钢材重多少千克？(得数保留两位小数)
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

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

<gadget id="calculator">7.8 / 1_000</gadget>
<output>0.0078</output>

<gadget id="calculator">3.14 * 100 * 2 * 100 * 0.0078</gadget>
<output>489.84</output>

<result>489.84</result>