A train needs to pass through 5 stations on the way from station A to station B, how many different train tickets should be prepared on the route of A and B?
一列火车从甲站行驶到乙站的途中需经过5个车站，则甲乙这条线路上需准备多少种不同的火车票．
<gadget id="calculator">6 + 5 + 4 + 3 + 2 + 1</gadget>
<output>21</output>

<result>21</result>