A rectangular concrete floor has a perimeter of 30 meters and its length and width are prime numbers. How many square meters is this concrete floor?
一块长方形的水泥地，它的周长是30米，长和宽都是质数．这块水泥地面积是多少平方米？
<gadget id="calculator">13 * 2</gadget>
<output>26</output>

<result>26</result>