|시간 제한||메모리 제한||제출||정답||맞은 사람||정답 비율|
|2 초||512 MB||1||1||1||100.000%|
A polyomino is a connected set of unit squares on a square grid. The picture below shows 4 examples of polyominoes.
Polyomino is called convex if its intersection with any vertical or horizontal line is a segment. The picture above shows two convex polyominoes (a) and (b) and two non-convex ones (c) and (d).
Two squares are called adjacent if they share a common side. It is easy to see that for any two squares of a convex polyomino it is possible to get from any square to any other one moving from a square to adjacent one and using only two directions. The picture below shows an example of such path for polyomino (b).
For a convex polyomino $P$ let us define its jinxiety $J(P)$ as a minimal $k$ such that it is possible to get from any square to any other square by a path that uses two directions and makes at most $k$ turns. For example, the polyomino (a) has jinxiety of 1 and polyomino (b) has jinxiety of 2.
Given a convex polyomino you have to find its jinxiety.
The input file contains multiple test cases.
Each test case contains two integers $h$ and $w$ --- the number of rows and columns in polyomino description, respectively ($1 \le h, w \le 2000$).
The following $h$ lines contain $w$ characters each and describe the polyomino. Each character is either "
." for an empty square, or "
#" for a polyomino square. It is guaranteed that the described figure is a convex polyomino.
Input is followed by a line with $h = w = 0$. The total number of characters in all polyomino descriptions of the input file is at most $4\cdot10^6$. There are at most $40\,000$ tests.
For each test case print one integer: the jinxiety of the polyomino in the input.
4 5 ##### ##### ###.. ##... 5 5 ####. .#### ..### ...## ...## 0 0