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 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.

Output

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

Constraints

$1 \le n \le 2500$

$1 \le m \le 5000$

$1 \le a,b \le n$

$-10^$9 \le x \le 10^9$

Example

Input

4 5
1 2 3
2 4 -1
1 3 -2
3 4 7
1 4 4

Output

5