from collections import deque

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

ci, cj = None, None
for i in range(h):
    for j in range(w):
        if S[i][j] == '.':
            ci, cj = i, j
            break
    if ci is not None:
        break

Directions = [(1, 0), (0, 1), (-1, 0), (0, -1)]
Que = deque([(ci, cj)])
start_set = set()
start_set.add((ci, cj))
while Que:
    ci, cj = Que.popleft()
    for di, dj in Directions:
        ni, nj = ci + di, cj + dj
        if 0 <= ni < h and 0 <= nj < w:
            if S[ni][nj] == '.' and (ni, nj) not in start_set:
                start_set.add((ni, nj))
                Que.append((ni, nj))

Que = deque()
for ci, cj in start_set:
    Que.append((ci, cj, 0))
seen = set()
while Que:
    ci, cj, cnt = Que.popleft()
    if S[ci][cj] == '.' and (ci, cj) not in start_set:
        print(cnt - 1)
        break
    for di, dj in Directions:
        ni, nj = ci + di, cj + dj
        if 0 <= ni < h and 0 <= nj < w:
            if (ni, nj) not in start_set and (ni, nj) not in seen:
                seen.add((ni, nj))
                Que.append((ni, nj, cnt + 1))