There are 6 yellow balls, 6 red balls, and 6 white balls in the box. At least how many balls can be drawn to ensure that there must be three colors in the drawn balls.
盒子里有黄球、红球、白球各6个，至少摸出多少个球就能保证摸出的球中一定有三种颜色．
<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">12 + 1</gadget>
<output>13</output>

<result>13</result>