Scavenger Hunt

Your girlfriend (boy friend) set up a scavengers hunt for you to
follow. An array A[0..n-1] contains the sequence of pointers to the
treasure.  A[0] is the first cell to look in.  A[0] contains the index
i1 to look in next.  A[i1] contains the index i2 to look in after
that. Follow this chain until you find A[i*] containing a zero. Note
that the array A may contain other zeros. They are not for
you. Sometimes you will be sent on a wild goose chase. 

For example, if n=10 and the array contents are
8 4 0 6 7 9 2 5 3 0
0 1 2 3 4 5 6 7 8 9  (indexes not part of the input)
Here, the treasure is located at index 2.

An example of a wild goose chase is the following array (again with n=10):
9 0 0 0 5 9 0 0 0 4
0 1 2 3 4 5 6 7 8 9  (indexes not part of the input)

Any input that causes you to reach an index that is out of range (less
than 0 or larger than n-1) is also considered a wild goose chase.

Input:

The input contains a number of examples. Each example consists of the
size n of the array on one line and the contents of the array on the
next.  n<=100. The instances will be
terminated with n=0.

Output:

For each input instance, the output is the index i* of your prize. 
If it was a wild goose chase, output -1.

Sample Input:

10
8 4 0 6 7 9 2 5 3 11
10
9 0 0 0 5 9 0 0 0 4
5
2 0 -1 1 3
0

Sample Output:

2
-1
-1