A cylindrical tin bucket without a lid is 20 cm high and 20 cm in diameter at the bottom. How many square centimeters of tin should be used to make this bucket? (interface not counted)
一个没有盖的圆柱形铁皮水桶，高是20厘米，底面直径是20厘米，做这个水桶至少要用铁皮多少平方厘米？(接口处不计)
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

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

<gadget id="calculator">3.14 * 100</gadget>
<output>314</output>

<gadget id="calculator">3.14 * 20 * 20</gadget>
<output>1_256</output>

<gadget id="calculator">314 + 1_256</gadget>
<output>1_570</output>

<result>1_570</result>