To make a cylindrical iron bucket with a bottom diameter of 4 decimeters and a height of 5 decimeters, at least how many iron sheets are needed.
做一个底面直径4分米，高5分米的圆柱形无盖铁皮水桶，至少需要多少铁皮．
<gadget id="calculator">3.14 * 4 * 5</gadget>
<output>62.8</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<gadget id="calculator">62.8 + 12.56</gadget>
<output>75.36</output>

<result>75.36</result>