Paint a house pillar with a height of 4 meters and a diameter of 4 decimeters at the bottom. What is the painted area?
油漆一根高为4米，底面直径为4分米的房柱子，油漆面积是多少．
<gadget id="calculator">4 * 10</gadget>
<output>40</output>

<gadget id="calculator">3.14 * 4 * 40</gadget>
<output>502.4</output>

<result>502.4</result>