There are 11, 10, and 9 balls in each of red, yellow, and green balls. How many balls should you touch at least to ensure that there are two green balls?
有红，黄，绿三种球各有11个，10个，9个，至少摸几个球才能保证有两个绿球？
<gadget id="calculator">11 + 10 + 2</gadget>
<output>23</output>

<result>23</result>