There are 4 stations in the long-distance bus from Shanghai to Suzhou. How many different tickets do you need to prepare for this long-distance bus from Shanghai to Suzhou?
从上海到苏州的长途汽车中共有4个车站，从上海到苏州需要为这趟长途汽车备多少种不同的车票．
<gadget id="calculator">5 + 4 + 3 + 2 + 1</gadget>
<output>15</output>

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

<result>30</result>