from collections import deque
W, H = map(int,input().split())
C = [input() for _ in range(H)]
INF=float('inf')
visited = [[-1] * W for _ in range(H)]

def group(val):
  for i in range(H):
    for j in range(W):
      if C[i][j] == "." and visited[i][j] == -1:
        si = i
        sj = j

  directions=[
    (1,0),
    (-1,0),
    (0,1),
    (0,-1),
  ]

  visited[si][sj] = val
  que = deque()
  que.append((si, sj))

  while que:
    i, j = que.popleft()
    for di, dj in directions:
      ni = i + di
      nj = j + dj
      if not (0 <= ni < H and 0 <= nj < W):
        continue

      if C[ni][nj] == "#":
        continue

      if visited[ni][nj] != -1:
        continue

      visited[ni][nj] = val
      que.append((ni, nj))


# 1つ目の空洞
group(0)
# 2つ目の空洞
group(INF)

# 一方からもう一方へ向かう
que = deque()
for i in range(H):
  for j in range(W):
    if visited[i][j] == 0:
      que.append((i, j))

directions=[
  (1,0),
  (-1,0),
  (0,1),
  (0,-1),
]

ans = INF
while que:
  i, j = que.popleft()
  for di, dj in directions:
    ni = i + di
    nj = j + dj

    if not (0 < ni < H-1 and 0 < nj < W-1):
      continue

    if visited[ni][nj] == INF:
      ans = min(ans, visited[i][j])
      continue

    if C[ni][nj] != "#":
      continue

    if visited[ni][nj] != -1 and visited[ni][nj] <= visited[i][j] + 1:
      continue

    visited[ni][nj] = visited[i][j] + 1
    que.append((ni, nj))

print(ans)