There are 3 balls of two colors, yellow and red, and put them in the same box. At least how many balls are taken to ensure that 2 balls of the same color are taken.
有黄、红两种颜色的球各3个，放到同一个盒子里，至少取多少个球可以保证取到2个颜色相同的球．
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<result>3</result>