Description
There is a 
grid. Each cell is either an empty cell or a wall. You are on 
in the beginning and want to go to 
.
It's guaranteed that and are empty cells.
You could move to an adjacent empty cell (i.e an empty cell which shares a common side with the cell which you are on).
Find the minimum number of cells you need to pass by to reach . There may be no such a path for you to reach .
Input
The first line contains two positive integers 
and 
– the size of the grid.
Then lines folllow. The 
-th line contains 
characters. The 
-th characters in the 
-th line 
may be 0 or 1. The cell 
is an empty cell if 
is equal to 0. Otherwise it's a wall.
The next line contains two integers 
and 
– the initial cell you are on.
The final line contains two integers 
and 
– the cell you want to go.
Note that and must be empty cells. Also they are different(i.e 
or 
).
It's guaranteed that:
- The 1st testcase must be identical to the Sample #1 below
- For the first 5 testcases:
- For the first 7 testcases:
Output
Output the minimum cells you must pass by for you to reach 
. Output -1 instead if there is no such a path.
Remember to print a newline('\n') character at the end of the line.
Note: there are two sample below. "# Sample Input 1/2" and "# Sample Output 1/2" are not the part of input and output.
They are just for marking that the following content corresponds to which sample.