There are some children, and each of them has at most 3 friends. Among these children, they are either their friends or their friends' friends. How many children do they have at most?
有一些小朋友，他们每个人最多有3个朋友，在这些小朋友中不是自己的朋友就是自己朋友的朋友，请问最多有几个小朋友．
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">9 + 1</gadget>
<output>10</output>

<result>10</result>