Use 20 1-meter-long wooden sticks to surround a rectangular vegetable field against a wall. What is the maximum area of the enclosed vegetable field?
用20根1米长的木条靠一面墙围一块长方形菜地，围成的菜地面积最大是多少．
<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">10 * 5</gadget>
<output>50</output>

<result>50</result>