To make a cylindrical tin bucket without a cover, the diameter of the bottom surface is 40 cm, and the height of the bucket is 50 cm. How many square centimeters of tin should be used to make such a bucket?
做一个无盖的圆柱形铁皮水桶，底面直径是40厘米，水桶高50厘米，做一个这样的水桶至少要用多少平方厘米的铁皮？
<gadget id="calculator">3.14 * 40 * 50</gadget>
<output>6_280</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

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

<gadget id="calculator">3.14 * 400</gadget>
<output>1_256</output>

<gadget id="calculator">6_280 + 1_256</gadget>
<output>7_536</output>

<result>7_536</result>