写一个程序，帮助前来咨询的游客找一条出发地和目的地之间的最短路径。如果有若干条路径都是最短的，那么需要输出最便宜的一条路径。(Write a program that helps visitors come to the shortest path between a destination and a destination. If there are several paths that are shortest, then you need to output the cheapest path.)