There are 28 balls of three different colors in a bag, including 12 red balls, 9 black balls, and 7 white balls. If you want to ensure that there are at least 5 balls of the same color and 4 balls of the same color in the bag Balls, then, how many balls can be taken out at most.
一个袋里放了三种颜色不同的28个球，其中红球12个，黑球9个，白球7个，如果要保证袋里至少还有5个同色球以及4个另一种颜色的同色球，那么，最多能取出多少个球．
<gadget id="calculator">12 - 5</gadget>
<output>7</output>

<gadget id="calculator">9 - 5</gadget>
<output>4</output>

<gadget id="calculator">12 - 5 - 5 - 4</gadget>
<output>-2</output>

<gadget id="calculator">7 + 4 + (-2)</gadget>
<output>9</output>

<result>9</result>