There are 10 red, yellow and white balls of the same size in a box, and at least how many balls are taken out can ensure that there are three colored balls.
一个盒子里面放了大小相同的红、黄、白三种颜色球各10个，至少拿出多少个球就能保证有三种颜色的球．
<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<result>21</result>