There are 4 red balls and 4 yellow balls of the same size in the box. If you want to draw the balls, there must be 2 balls of the same color. The minimum number of balls you need to draw.
盒子里有同样大小的红球和黄球各4个，要想摸出的球一定有2个同色的，最少要摸出多少个球．
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<result>3</result>