There are 10 black balls, 15 white balls and 20 red balls in a pocket, at least how many balls are taken from it, and it is guaranteed that there are white balls among them.
在一个口袋里有10个黑球，15个白球和20个红球，至少从中取出多少个球，能保证其中有白球．
<gadget id="calculator">20 + 10 + 1</gadget>
<output>31</output>

<result>31</result>