The express train between Shanghai and Nanjing depends on 6 stations besides the starting point and the ending point. How many kinds of tickets should be prepared for the car?
上海与南京之间的快车，除起点、终点外，还要靠6个站点，汽车要准备多少种车票．
<gadget id="calculator">7 + 6 + 5 + 4 + 3 + 2 + 1</gadget>
<output>28</output>

<gadget id="calculator">28 * 2</gadget>
<output>56</output>

<result>56</result>