import typing


class DSU:
    '''
    Implement (union by size) + (path halving)

    Reference:
    Zvi Galil and Giuseppe F. Italiano,
    Data structures and algorithms for disjoint set union problems
    '''

    def __init__(self, n: int = 0) -> None:
        self._n = n
        self.parent_or_size = [-1] * n

    def merge(self, a: int, b: int) -> int:
        assert 0 <= a < self._n
        assert 0 <= b < self._n

        x = self.leader(a)
        y = self.leader(b)

        if x == y:
            return x

        if -self.parent_or_size[x] < -self.parent_or_size[y]:
            x, y = y, x

        self.parent_or_size[x] += self.parent_or_size[y]
        self.parent_or_size[y] = x

        return x

    def same(self, a: int, b: int) -> bool:
        assert 0 <= a < self._n
        assert 0 <= b < self._n

        return self.leader(a) == self.leader(b)

    def leader(self, a: int) -> int:
        assert 0 <= a < self._n

        parent = self.parent_or_size[a]
        while parent >= 0:
            if self.parent_or_size[parent] < 0:
                return parent
            self.parent_or_size[a], a, parent = (
                self.parent_or_size[parent],
                self.parent_or_size[parent],
                self.parent_or_size[self.parent_or_size[parent]]
            )

        return a

    def size(self, a: int) -> int:
        assert 0 <= a < self._n

        return -self.parent_or_size[self.leader(a)]

    def groups(self) -> typing.List[typing.List[int]]:
        leader_buf = [self.leader(i) for i in range(self._n)]

        result: typing.List[typing.List[int]] = [[] for _ in range(self._n)]
        for i in range(self._n):
            result[leader_buf[i]].append(i)

        return list(filter(lambda r: r, result))


W, H = map(int, input().split())
C = [input() for _ in range(H)]
dsu = DSU(H * W)
D = []
for h in range(H):
    for w in range(W):
        hw = h * W + w
        if C[h][w] == ".":
            D.append(hw)
            if h > 0:
                if C[h - 1][w] == ".":
                    dsu.merge(hw, (h - 1) * W + w)
            if w > 0:
                if C[h][w - 1] == ".":
                    dsu.merge(hw, hw - 1)
l0 = dsu.leader(D[0])
l1 = -1
q = []
for d in D:
    if dsu.leader(d) == l0:
        q.append(d)
    else:
        l1 = dsu.leader(d)
#print(sorted(q))
def merge(x):
    global q2
    if not dsu.same(x, l0):
        dsu.merge(x, l0)
        q2.add(x)


lead = []
cnt = 0
cnt = 0
while not dsu.same(l0,l1):
    q2 = set()
    while q:
        x = q.pop()
        if x >= W:
            y = x - W
            merge(y)
        if x < (H -1) * W:
            y = x + W
            merge(y)
        if x % W != 0:
            y = x - 1
            merge(y)
        if x % W != W - 1:
            y = x + 1
            merge(y)
    q = list(q2)
    #print(cnt,sorted(q))
    cnt += 1
print(cnt-1)