CSES - Distinct Routes II
  • Time limit: 1.00 s
  • Memory limit: 512 MB
A game consists of $n$ rooms and $m$ teleporters. At the beginning of each day, you start in room $1$ and you have to reach room $n$.

You can use each teleporter at most once during the game. You want to play the game for exactly $k$ days. Every time you use any teleporter you have to pay one coin. What is the minimum number of coins you have to pay during $k$ days if you play optimally?


The first input line has three integers $n$, $m$ and $k$: the number of rooms, the number of teleporters and the number of days you play the game. The rooms are numbered $1,2,\dots,n$.

After this, there are $m$ lines describing the teleporters. Each line has two integers $a$ and $b$: there is a teleporter from room $a$ to room $b$.

There are no two teleporters whose starting and ending room are the same.


First print one integer: the minimum number of coins you have to pay if you play optimally. Then, print $k$ route descriptions according to the example. You can print any valid solution.

If it is not possible to play the game for $k$ days, print only -1.

  • $2 \le n \le 500$
  • $1 \le m \le 1000$
  • $1 \le k \le n-1$
  • $1 \le a,b \le n$

8 10 2
1 2
1 3
2 5
2 4
3 5
3 6
4 8
5 8
6 7
7 8

1 2 4 8
1 3 5 8