sealed opaque bag contains three balls of red, yellow, and blue colors. If you want to draw out the balls, there must be two balls of the same color. At least how many balls must be drawn out.
一个密封的不透明的袋子里装了红、黄、蓝三种颜色的球各3个，要想摸出的球一定有两个球是同色的，至少要摸出多少个球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>