To make a cylindrical oil barrel with a base radius of 5 decimeters and a height of 4 decimeters, how much iron sheet should be used at least?
制做一个底面半径为5分米、高为4分米的圆柱形油桶，至少要用多大面积的铁皮？
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25 * 2</gadget>
<output>157</output>

<gadget id="calculator">3.14 * 5 * 2 * 4</gadget>
<output>125.6</output>

<gadget id="calculator">157 + 125.6</gadget>
<output>282.6</output>

<result>282.6</result>