Put 5 red, white, and blue balls into a box, and at least how many balls are taken each time to ensure that there must be two balls of the same color.
把红色、白色、蓝色三种球各5个放进一个盒子里，每次至少拿多少个球可以保证一定有两个球是同一种颜色的．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>