A garden with a length of 30 meters and a width of 20 meters has a square pool with a circumference of 8 meters in the middle. How much can the garden be greened?
一个长30米，宽20米的花园，中间做了一个周长8米的正方形水池，求花园可绿化面积有多大？
<gadget id="calculator">30 * 20</gadget>
<output>600</output>

<gadget id="calculator">8 / 4</gadget>
<output>2</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">600 - 4</gadget>
<output>596</output>

<result>596</result>