There are 30 balls of the same size in a box, including 10 red ones, 8 white ones, 7 yellow ones, and 5 green ones. Don't look at it with your eyes, at least how many balls are taken out to ensure that there must be 7 balls of the same color.
一盒子里有同样大小的球30个，其中红的10个、白的8个、黄的7个、绿的5个．不用眼睛看，至少取出多少个球，才能保证一定有7个颜色相同的球．
<gadget id="calculator">6 + 6 + 5 + 6 + 1</gadget>
<output>24</output>

<result>24</result>