A rectangular paper with a length of 20 cm and a width of 10 cm is rolled into the largest cylinder. When the height is 20 cm, what is the area of the side?
长20cm，宽10cm的长方形纸，卷成最大的圆柱，当高是20cm时，侧面的面积是多少？
<gadget id="calculator">20 * 10</gadget>
<output>200</output>

<result>200</result>