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? \InputFile The first line has two integers $n\:(1 \le n \le 2500)$ and $m\:(1 \le m \le 5000)$: 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 $a$, $b\:(1 \le a, b \le n)$ and $x\:(−10^9 \le x \le 10^9)$: 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 $n$. \OutputFile Print one integer: the maximum score you can get. However, if you can get an arbitrarily large score, print $-1$.