There are 4 balls of different colors in a bag, including 10 red balls, 9 blue balls, 8 yellow balls, and 7 white balls. What is the minimum number of balls that someone can take out of the bag with his eyes closed to ensure that there are 4 balls of different colors? have.
一个袋子里有4种不同颜色的球，其中红球10个，蓝球9个，黄球8个，白球7个，某人闭着眼睛从中最少取出多少个球，才能保证4种颜色的球都有．
<gadget id="calculator">10 + 9 + 8 + 1</gadget>
<output>28</output>

<result>28</result>