import itertools
from collections import deque

W, H = map(int, input().split())
C = [input() for _ in range(H)]

table = [[None] * W for _ in range(H)]
for h, w in itertools.product(range(1, H - 1), range(1, W - 1)):
    if C[h][w] == '.':
        h0, w0 = h, w
        break

# bfs(連結部分)
D0 = deque([(h0, w0)])
D = deque()
table[h0][w0] = 0
while D0:
    h, w = D0.popleft()
    for dh, dw in ((1, 0), (-1, 0), (0, 1), (0, -1)):
        if 0 <= h + dh < H and 0 <= w + dw < W and table[h + dh][w + dw] is None:
            if C[h + dh][w + dw] == '.':
                D0.append((h + dh, w + dw))
                table[h + dh][w + dw] = 0
            else:
                D.append((h + dh, w + dw))
                table[h + dh][w + dw] = 1
# bfs(壁)
while D:
    h, w = D.popleft()
    for dh, dw in ((1, 0), (-1, 0), (0, 1), (0, -1)):
        if 0 <= h + dh < H and 0 <= w + dw < W and table[h + dh][w + dw] is None:
            D.append((h + dh, w + dw))
            if C[h + dh][w + dw] == '.':
                print(table[h][w])
                exit()
            else:
                table[h + dh][w + dw] = table[h][w] + 1