There are 4 small balls of red, yellow, blue and green in the cloth bag. In order to ensure that two small balls of the same color can be taken out at one time, at least how many small balls must be drawn out at one time.
布袋中装有红、黄、蓝、绿四种颜色的小球各4个，为保证一次能取出两个颜色相同的小球，一次至少要摸出多少个小球．
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<result>5</result>