There are 8 red balls, 6 white balls, 4 green balls, and 1 black ball in a box, how many balls must be taken out to ensure that the taken out balls have at least three different colors.
一个箱子里有8个红球，6个白球，4个绿球，1个黑球，则至少要取出多少个球才能保证取出的球至少有三种不同的颜色．
<gadget id="calculator">8 + 6 + 1</gadget>
<output>15</output>

<result>15</result>