There are 5 red, yellow and white balls in the box, how many balls should be taken at least to ensure that there are 2 balls of the same color.
盒子里有红、黄、白球各5个，至少取多少个，才能保证有2个球同色．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>