There are 4 red balls, 4 yellow balls and 1 white ball 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4个红球、4个黄球和一个白球，要想摸出的球一定有2个同色的，最少要摸出多少球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>