Given an undirected graph with n vertices via its adjacency matrix, and

two vertices s and t, determine the length of the shortest path between

s and t, measured as the number of edges.

If s == t, the answer is 0. If no path exists between s

and t, print -1.

Input:

The first line contains three natural numbers, n, s and t, separated by

spaces. The following n lines each contain n binary values: the adjacency

matrix.

- 1 <= n <= 50

- 1 <= s, t <= n

- use breadth-first search (BFS) implemented with an array

Output:

The program prints to standard output a single integer: the minimum path length from

s to t, or -1 if the two vertices are not in the same

connected component.

Example:

Input:

6 1 6

0 1 1 0 0 0

1 0 0 1 0 0

1 0 0 1 0 0

0 1 1 0 1 0

0 0 0 1 0 1

0 0 0 0 1 0

Output:

4