There are 20 balls of 3 different colors in a bag, 8 of which are white, 7 are red, and 5 are green. If you close your eyes and take out balls from the bag, it is required that there are at least 4 balls of the same color and 3 balls of another color among the remaining balls in the bag, then how many balls can only be taken at most.
一个袋子里面放了3种不同颜色的球共20个，其中8个白色的，7个红色的，5个绿色的．如果闭上眼睛从袋子里取出球，要求袋子中剩下的球中至少有4个同色的球和3个另一种颜色的球，那么最多只能取多少个球．
<gadget id="calculator">8 - 4</gadget>
<output>4</output>

<gadget id="calculator">7 - 4</gadget>
<output>3</output>

<gadget id="calculator">5 - 4 - 3</gadget>
<output>-2</output>

<gadget id="calculator">4 + 3 + (-2)</gadget>
<output>5</output>

<result>5</result>