Close to a fence, use an 18-meter-long bamboo fence to enclose a rectangular (side length is an integer) vegetable field. What is the maximum area of this vegetable field in square meters?
紧靠一道围墙边，用18米长的竹篱笆围出一块长方形(边长为整数)的菜地，这块菜地的面积最大是多少平方米．
<gadget id="calculator">8 * 5</gadget>
<output>40</output>

<result>40</result>