A8655 | Cutting Figure

You've gotten an $n×m$ sheet of squared paper. Some of its squares are painted. Let's mark the set of all painted squares as $A$ . Set $A$ is connected. Your task is to find the minimum number of squares that we can delete from set $A$ to make it not connected.

A set of painted squares is called connected, if for every two squares $a$ and $b$ from this set there is a sequence of squares from the set, beginning in $a$ and ending in $b$ , such that in this sequence any square, except for the last one, shares a common side with the square that follows next in the sequence. An empty set and a set consisting of exactly one square are connected by definition.

The first input line contains two space-separated integers $n$ and $m$ ( $1<=n,m<=50$ ) — the sizes of the sheet of paper.

Each of the next $n$ lines contains $m$ characters — the description of the sheet of paper: the $j$ -th character of the $i$ -th line equals either "#", if the corresponding square is painted (belongs to set $A$ ), or equals "." if the corresponding square is not painted (does not belong to set $A$ ). It is guaranteed that the set of all painted squares $A$ is connected and isn't empty.

On the first line print the minimum number of squares that need to be deleted to make set $A$ not connected. If it is impossible, print -1.