class UnionFind:
    def __init__(self, n):
        self.par = [-1]*n
        self.rank = [0]*n

    def Find(self, x):
        if self.par[x] < 0:
            return x
        else:
            self.par[x] = self.Find(self.par[x])
            return self.par[x]

    def Unite(self, x, y):
        x = self.Find(x)
        y = self.Find(y)

        if x != y:
            if self.rank[x] < self.rank[y]:
                self.par[y] += self.par[x]
                self.par[x] = y
            else:
                self.par[x] += self.par[y]
                self.par[y] = x
                if self.rank[x] == self.rank[y]:
                    self.rank[x] += 1

    def Same(self, x, y):
        return self.Find(x) == self.Find(y)

    def Size(self, x):
        return -self.par[self.Find(x)]

from collections import deque
INF = 10**18

w, h = map(int, input().split())
C = [str(input()) for i in range(h)]
uf = UnionFind(h*w)
for y in range(h):
    for x in range(w):
        if C[y][x] == '#':
            continue
        for dy, dx in (-1, 0), (1, 0), (0, 1), (0, -1):
            ny, nx = y+dy, x+dx
            if 0 <= ny < h and 0 <= nx < w:
                if C[ny][nx] != '#':
                    uf.Unite(y*w+x, ny*w+nx)

for y in range(h):
    for x in range(w):
        if C[y][x] != '#':
            p = y*w+x
            break
    else:
        continue
    break

q = deque([])
dist = [[INF]*w for i in range(h)]
for y in range(h):
    for x in range(w):
        if C[y][x] == '#':
            continue
        if uf.Same(p, y*w+x):
            q.append((y, x))
            dist[y][x] = 0
while q:
    y, x = q.popleft()
    for dy, dx in (-1, 0), (1, 0), (0, 1), (0, -1):
        ny, nx = y+dy, x+dx
        if 0 <= ny < h and 0 <= nx < w:
            if dist[ny][nx] == INF:
                dist[ny][nx] = dist[y][x]+1
                q.append((ny, nx))
ans = INF
for y in range(h):
    for x in range(w):
        if C[y][x] == '#':
            continue
        if not uf.Same(p, y*w+x):
            ans = min(ans, dist[y][x]-1)
print(ans)