- Time limit: 1.00 s
- Memory limit: 512 MB
You play a game consisting of n rooms and m tunnels. Your initial score is 0, and each tunnel increases your score by x where x may be both positive or negative. You may go through a tunnel several times.
Your task is to walk from room 1 to room n. What is the maximum score you can get?
The first input line has two integers n and m: the number of rooms and tunnels. The rooms are numbered 1,2,\dots,n.
Then, there are m lines describing the tunnels. Each line has three integers a, b and x: the tunnel starts at room a, ends at room b, and it increases your score by x. All tunnels are one-way tunnels.
You can assume that it is possible to get from room 1 to room n.
Print one integer: the maximum score you can get. However, if you can get an arbitrarily large score, print -1.
- 1 \le n \le 2500
- 1 \le m \le 5000
- 1 \le a,b \le n
- -10^9 \le x \le 10^9
4 5 1 2 3 2 4 -1 1 3 -2 3 4 7 1 4 4