There are 6 red, yellow, and blue balls in a cloth bag. How many balls can be touched at a time to ensure that 2 of them are of the same color.
在一个布袋里有红色、黄色、蓝色小球各6个，一次至少摸出多少只才能保证其中有2个是同色的．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>