There are 3 red balls, 3 yellow balls and 1 white ball of the same size in the box. If you want to draw balls, there must be 2 balls of the same color. How many balls must be drawn at least.
盒子里有同样大小的3个红球，3个黄球和一个白球，要想摸出的球一定有2个是同色的，最少要摸出多少个球．
<gadget id="calculator">1 + 2 + 1</gadget>
<output>4</output>

<result>4</result>