There are 5 small balls of red, yellow, and blue colors, and they are mixed in a shadow box. At least how many balls can be drawn at a time to ensure that there are 2 small balls of the same color.
有红、黄、蓝三种颜色的小球各5个，混合放在一个暗盒里，一次至少摸出多少个才能保证有2个小球是同色的．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>