There are 10 red, white and blue balls in a bag, at least how many balls are taken out to ensure that there are two balls of the same color.
一个袋子里有红、白、蓝三种颜色的球各10个，至少拿出多少个球才能保证有两个颜色相同的球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>