To make a cylindrical keg with a height of 10dm and a bottom diameter of 50cm, how many cm**2 iron sheets are needed?
做一个高是10dm，底面直径是50cm的无盖的圆柱形小桶，需要多少cm**2的铁皮．
<gadget id="calculator">50 / 2</gadget>
<output>25</output>

<gadget id="calculator">25 ** 2</gadget>
<output>625</output>

<gadget id="calculator">3.14 * 625</gadget>
<output>1_962.5</output>

<gadget id="calculator">3.14 * 50 * 10 * 10</gadget>
<output>15_700</output>

<gadget id="calculator">1_962.5 + 15_700</gadget>
<output>17_662.5</output>

<result>17_662.5</result>