from collections import deque
INF = 1000
W, H = map(int, input().split())
C = [list(input()) for _ in range(H)]

def check(i, j):
    return 0 <= i < H and 0 <= j < W

for i in range(H):
    for j in range(W):
        if C[i][j] == '.':
            si, sj = i, j
            break
    else:
        continue
    break

# si, sj から 01BFS
dist = [[INF] * (W) for _ in range(H)]
dist[si][sj] = 0

que = deque()
que.append((si, sj))
while que:
    i, j = que.popleft()
    for ii, jj in [(0, -1), (0, 1), (-1, 0), (1, 0)]:
        ni, nj = i+ii, j+jj
        if check(ni, nj):
            # . だったら 0
            if C[ni][nj] == '.' and dist[ni][nj] > dist[i][j]:
                dist[ni][nj] = dist[i][j]
                que.appendleft((ni, nj))

            # # だったら 1
            if C[ni][nj] == '#' and dist[ni][nj] > dist[i][j] + 1:
                dist[ni][nj] = dist[i][j] + 1
                que.append((ni, nj))
# こたえ
for i in range(H):
    for j in range(W):
        if C[i][j] == '.' and dist[i][j] != 0:
            exit(print(dist[i][j]))