import sys

def input(): return sys.stdin.readline().strip()
def list2d(a, b, c): return [[c] * b for i in range(a)]
def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]
def list4d(a, b, c, d, e): return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]
def ceil(x, y=1): return int(-(-x // y))
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]
def Yes(): print('Yes')
def No(): print('No')
def YES(): print('YES')
def NO(): print('NO')
sys.setrecursionlimit(10 ** 9)
INF = 10 ** 19
MOD = 10 ** 9 + 7
EPS = 10 ** -10

def build_grid(H, W, intv, _type, space=True, padding=False):
    if space:
        _input = lambda: input().split()
    else:
        _input = lambda: input()
    _list = lambda: list(map(_type, _input()))
    if padding:
        offset = 1
    else:
        offset = 0
    grid = list2d(H+offset*2, W+offset*2, intv)
    for i in range(offset, H+offset):
        row = _list()
        for j in range(offset, W+offset):
            grid[i][j] = row[j-offset]
    return grid

def bfs1(grid, src):
    from collections import deque

    H, W = len(grid), len(grid[0])
    directions = ((1, 0), (-1, 0), (0, 1), (0, -1))
    dist = list2d(H, W, INF)
    que = deque()
    for h, w in src:
        que.append((h, w))
        dist[h][w] = 0
    while que:
        h, w = que.popleft()
        for dh, dw in directions:
            h2 = h + dh
            w2 = w + dw
            if dist[h2][w2] != INF:
                continue
            if grid[h2][w2] == '.':    
                dist[h2][w2] = dist[h][w]
                que.appendleft((h2, w2))
            elif grid[h2][w2] == '#':
                dist[h2][w2] = dist[h][w] + 1
                que.append((h2, w2))
    return dist

def bfs2(grid, dist, src):
    from collections import deque

    H, W = len(grid), len(grid[0])
    directions = ((1, 0), (-1, 0), (0, 1), (0, -1))
    visited = list2d(H, W, 0)
    que = deque()
    for h, w in src:
        que.append((h, w))
        visited[h][w] = 1
    res = INF
    while que:
        h, w = que.popleft()
        for dh, dw in directions:
            h2 = h + dh
            w2 = w + dw
            if visited[h2][w2]:
                continue
            if grid[h2][w2] == '.':    
                visited[h2][w2] = 1
                que.append((h2, w2))
            elif grid[h2][w2] == '#':
                visited[h2][w2] = 1
                res = min(res, dist[h2][w2])
    return res

W, H = MAP()
grid = build_grid(H, W, '*', str, space=0, padding=1)

done = False
for i in range(1, H+1):
    for j in range(1, W+1):
        if grid[i][j] == '.':
            dist = bfs1(grid, [(i, j)])
            done = True
        if done:
            break
    if done:
        break

done = False
for i in range(1, H+1):
    for j in range(1, W+1):
        if grid[i][j] == '.' and dist[i][j] != 0:
            ans = bfs2(grid, dist, [(i, j)])
            done = True
        if done:
            break
    if done:
        break
print(ans)