There are 10 pencils of each of the three colors in the cloth bag (the pens of the three colors are completely mixed in the cloth bag), at least how many pencils can be taken out to ensure that all the pens of the three colors can be taken.
布袋里装有三种颜色的铅笔各10支(三种颜色的笔完全混放在布袋里)，至少取出多少支才能保证三种颜色的笔都取到．
<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<result>21</result>