Put 5 black balls and 4 flower balls in a pocket. 7 red balls, to ensure that black balls must be touched, at least how many balls must be touched.
一个口袋里放5个黑球，4个花球．7个红球，要确保一定摸到黑球，至少要摸多少个球．
<gadget id="calculator">4 + 7 + 1</gadget>
<output>12</output>

<result>12</result>