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 $-1$ .
4 5 1 2 3 2 4 -1 1 3 -2 3 4 7 1 4 4· \n · · \n · · \n · · \n · · \n · · \n
5\n