Minimum Steps in a Grid

Given an m × n grid where each cell is either open (0) or blocked (1), your task is to compute the minimum number of steps required to move from the top-left cell (0, 0) to the bottom-right cell (m-1, n-1) avoiding obstacles. You may move one step at a time in any of the four cardinal directions (up, down, left, right).

If the destination is not reachable, return -1.

The movement can be formulated as finding the shortest path in a grid, where each valid move has a cost of 1. In mathematical terms, if you denote the number of steps by \(s\), find the minimum \(s\) such that:

\[ (0,0) \rightarrow (m-1, n-1) \text{ using valid moves}, \]

Note that both the starting cell and the destination cell must be open.

inputFormat

The input is given via standard input (stdin) and consists of:

1. A line containing two integers m and n, the number of rows and columns respectively.
2. Followed by m lines, each containing n space-separated integers (either 0 or 1) representing the grid.

outputFormat

Output a single integer to standard output (stdout): the minimum number of steps from the start to the destination. If there is no valid path, output -1.

## sample

3 3
0 0 0
1 0 1
0 0 0

4