There are 5 red, yellow and blue balls in a bag, how many balls are taken each time to ensure that there are 2 balls of the same color.
一个袋子里有红、黄、蓝色三种球各5个，每次至少拿多少个才能保证有2个相同颜色的球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>