Xiaoqiang's father made a cylindrical storage barrel with a height of 50cm and a diameter of 40cm at the bottom with iron sheet. There is a mouth with a diameter of 20cm on the upper bottom. How many square centimeters of iron sheet should be used to make this storage barrel?
小强的爸爸用铁皮做了一个高50cm，底面直径40cm的圆柱形储物桶，它的上底留有一个直径是20cm的口，做这个储物桶至少要用铁皮多少平方厘米？
<gadget id="calculator">3.14 * 40 * 50</gadget>
<output>6_280</output>

<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_768 - 314</gadget>
<output>3_454</output>

<gadget id="calculator">6_280 + 3_768 + 3_454</gadget>
<output>13_502</output>

<result>13_502</result>