w,h=map(int,input().split())
l=[list(input()) for i in range(h)]

n=h*w
connection=[[] for i in range(h*w)]
connection2=[[] for i in range(h*w)]

for i in range(h):
  for j in range(w):
    if l[i][j]=='.':
      if i!=0:
        connection2[i*w+j].append((i-1)*w+j)
        if l[i-1][j]=='.':
          connection[i*w+j].append((i-1)*w+j)
      if i!=h-1:
        connection2[i*w+j].append((i+1)*w+j)
        if l[i+1][j]=='.':
          connection[i*w+j].append((i+1)*w+j)
      if j!=0:
        connection2[i*w+j].append(i*w+j-1)
        if l[i][j-1]=='.':
          connection[i*w+j].append(i*w+j-1)
      if j!=w-1:
        connection2[i*w+j].append(i*w+j+1)
        if l[i][j+1]=='.':
          connection[i*w+j].append(i*w+j+1)
    else:
      if i!=0:
        connection2[i*w+j].append((i-1)*w+j)
      if i!=h-1:
        connection2[i*w+j].append((i+1)*w+j)
      if j!=0:
        connection2[i*w+j].append(i*w+j-1)
      if j!=w-1:
        connection2[i*w+j].append(i*w+j+1)

def bfs(v):
  distance=[-1]*n
  distance[v]=0
  next=connection[v]
  next2=set()
  visited=[-1]*n
  visited[v]=1
  visitct=1
  ct=0
  while len(next)!=0 and visitct!=n:
    ct+=1
    for i in range(len(next)):
      if visited[next[i]]==-1:
        distance[next[i]]=ct
        visited[next[i]]=1
        visitct+=1
        for j in range(len(connection[next[i]])):
          if visited[connection[next[i]][j]]==-1:
            next2.add(connection[next[i]][j])
    next=list(next2)
    next2=set()
  return distance

def bfs2(l):
  distance=[-1]*n
  next=set()
  next2=set()
  visited=[-1]*n
  visitct=0
  for i in range(len(l)):
    distance[l[i]]=0
    for j in range(len(connection2[l[i]])):
      next.add(connection2[l[i]][j])
    visited[l[i]]=1
    visitct=+1
  next=list(next)
  ct=0
  while len(next)!=0 and visitct!=n:
    ct+=1
    for i in range(len(next)):
      if visited[next[i]]==-1:
        distance[next[i]]=ct
        visited[next[i]]=1
        visitct+=1
        for j in range(len(connection2[next[i]])):
          if visited[connection2[next[i]][j]]==-1:
            next2.add(connection2[next[i]][j])
    next=list(next2)
    next2=set()
  return distance

for i in range(n):
  if len(connection[i])!=0:
    x=i
    break

L=bfs(x)
L2=[]
for i in range(n):
  if L[i]!=-1:
    L2.append(i)

ans=[]
L3=bfs2(L2)
for i in range(n):
  if L[i]==-1 and l[i//w][i%w]=='.':
    ans.append(L3[i]-1)

print(min(ans))