from collections import deque
INF = 1<<16
W,H = map(int,input().split())
C = [list(input()) for _ in range(H)]
x = 0
y = 0
for i in range(H):
    for j in range(W):
        if C[i][j] == '.':
            x = i
            y = j
Queue = deque()
Queue2 = deque()
Queue2.append((x, y))
cost = [[INF] * W for _ in range(H)]
dx = [1, -1, 0, 0]
dy = [0, 0, 1, -1]
while Queue2:
    x,y = Queue2.popleft()
    cost[x][y] = 0
    Queue.append((x, y))
    for i in range(4):
        nx,ny = x+dx[i],y+dy[i]
        if C[nx][ny] == '.' and cost[nx][ny] == INF:
            Queue2.append((nx, ny))
ans = INF
while Queue:
    x,y = Queue.popleft()
    for i in range(4):
        nx,ny = x+dx[i],y+dy[i]
        if nx < 0 or H <= nx or ny < 0 or W <= ny:
            continue
        if C[nx][ny] == '#' and cost[x][y] + 1 < cost[nx][ny]:
            cost[nx][ny] = cost[x][y] + 1
            Queue.append((nx, ny))
        elif C[nx][ny] == '.' and cost[nx][ny] == INF:
            ans = min(ans, cost[x][y])
print(ans)