class DisjointSet(object):
    def __init__(self, n):
        self.parent = list(range(n))
        self.rank = [0] * n
        self.num = n  # number of disjoint sets

    def union(self, x, y):
        self._link(self.find_set(x), self.find_set(y))

    def _link(self, x, y):
        if x == y:
            return
        self.num -= 1
        if self.rank[x] > self.rank[y]:
            self.parent[y] = x
        else:
            self.parent[x] = y
            if self.rank[x] == self.rank[y]:
                self.rank[y] += 1

    def find_set(self, x):
        xp = self.parent[x]
        if xp != x:
            self.parent[x] = self.find_set(xp)
        return self.parent[x]


def read_data():
    W, H = map(int, input().split())
    maze = [input().strip() for h in range(H)]
    return W, H, maze

import collections

def solve(W, H, maze):
    maze = [[c == '.' for c in row] for row in maze]
    djs = DisjointSet(W * H)
    for h in range(1, H-1):
        for w in range(1, W-1):
            pos = h * W + w
            if maze[h][w]:
                if maze[h-1][w]:
                    djs.union(pos, pos - W)
                if maze[h][w-1]:
                    djs.union(pos, pos - 1)
            else:
                djs.union(pos, 0)
    areas = collections.defaultdict(list)
    for h in range(1, H-1):
        for w in range(1, W-1):
            p = djs.find_set(h * W + w)
            if p:
                areas[p].append((h, w))
    a1, a2 = areas
    frontiers = areas[a1]
    dist = 0
    while frontiers:
        new_frontiers = []
        for (h, w) in frontiers:
            for nh, nw in [(h+1, w), (h-1, w), (h, w+1), (h, w-1)]:
                if nh < 0 or nh >= H or nw < 0 or nw >= W:
                    continue
                if djs.find_set(nh * W + nw) == a2:
                    return dist
                elif not maze[nh][nw]:
                    maze[nh][nw] = True
                    new_frontiers.append((nh, nw))
        frontiers = new_frontiers
        dist += 1

if __name__ == '__main__':
    W, H, maze = read_data()
    print(solve(W, H, maze))