A cylindrical tin bucket without a cover, if its side is expanded, it is exactly a square with a side length of 6.28 decimeters. How much iron sheet is needed to make this bucket?
一个无盖圆柱形铁皮水桶，把它的侧面展开正好是一个边长为6.28分米的正方形．制这个水桶至少需要多少铁皮？
<gadget id="calculator">6.28 * 6.28</gadget>
<output>39.4384</output>

<gadget id="calculator">6.28 / 3.14 / 2</gadget>
<output>1</output>

<gadget id="calculator">1 ** 2</gadget>
<output>1</output>

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

<gadget id="calculator">39.4384 + 3.14</gadget>
<output>42.5784</output>

<result>42.5784</result>