High Score

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?

Input

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 $n$.

Output

Print one integer: the maximum score you can get. However, if you can get an arbitrarily large score, print $-1$.

Examples