Part Acquisition    partacq.X

The cows have been sent on a mission through space to acquire a new
milking machine for their barn.  They are flying through a cluster
of stars containing N (1 <= N <= 50,000) planets, each with a trading
post.

The cows have determined which of K (1 <= K <= 1,000) types of
objects (numbered 1..K) each planet in the cluster desires, and
which products they have to trade. No planet has developed currency,
so they work under the barter system: all trades consist of each
party trading exactly one object (presumably of different types).

The cows start from Earth with a canister of high quality hay (item
1), and they desire a new milking machine (item K). Help them find
the best way to make a series of trades at the planets in the cluster
to get item K.  If this task is impossible, output -1.

PROBLEM NAME: partacq

INPUT FORMAT:

* Line 1: Two space-separated integers, N and K.

* Lines 2..N+1: Line i+1 contains two space-separated integers, a_i
        and b_i respectively, that are planet i's trading trading
        products. The planet will give item b_i in order to receive
        item a_i.

SAMPLE INPUT:

6 5
1 3
3 2
2 3
3 1
2 5
5 4

OUTPUT FORMAT:

* Line 1: One more than the minimum number of trades to get the
        milking machine which is item K (or -1 if the cows cannot
        obtain item K).

* Lines 2..T+1: The ordered list of the objects that the cows possess
        in the sequence of trades.

SAMPLE OUTPUT:

4
1
3
2
5

OUTPUT DETAILS:

The cows possess 4 objects in total: first they trade object 1 for
object 3, then object 3 for object 2, then object 2 for object 5.