There are 6 red, white and black glass balls (these balls are the same except for the color) in each box. Linlin touches the balls arbitrarily, at least how many balls can be touched to ensure that there must be two glass balls of the same color?
箱子里有红色、白色和黑色的玻璃球(这些球除颜色外其他都相同)各6个．琳琳任意摸球，至少摸几个才能保证其中必有两个玻璃球的颜色相同？
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>