This is an unusual problem in an unusual contest, here is the announcement: http://codeforces.com/blog/entry/73543
Find the distance between vertices $$$1$$$ and $$$n$$$ in an undirected weighted graph.
The first line contains two integers $$$n, m$$$ ($$$1 \leq n, m \leq 2 \cdot 10^5$$$) — the number of vertices and the number of edges.
Each of the next $$$m$$$ lines contain description of an edge $$$a_i~b_i~cost_i$$$ ($$$1 \leq a_i, b_i \leq n$$$, $$$1 \leq cost_i \leq 10^9$$$).
Loops and multiple edges? Hmm, why not?
Print one integer — the answer to the problem. If there is no path, print $$$-1$$$ instead.
3 3 1 2 5 2 3 1 1 3 7