The high-speed railway from Quzhou to Hangzhou has 6 stops from the starting point to the ending point. How many kinds of tickets should be prepared for the round trip?
衢州至杭州的高铁从起点到终点共要停靠6个站，往返共要准备多少种车票．
<gadget id="calculator">5 + 4 + 3 + 2 + 1</gadget>
<output>15</output>

<gadget id="calculator">2 * 15</gadget>
<output>30</output>

<result>30</result>