Put 18 balls of each of the three colors of yellow, blue, and white into a bag, and at least how many balls are taken. It is guaranteed to get two balls of the same color.
把黄、蓝、白三种颜色的球各18个放到一个袋子里，至少取多少个球．可以保证取到颜色相同的两个球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>