# D - Maze Master
import copy
from collections import deque


def bfs(s, f):
    f[s[0]][s[1]] = 0
    moves = [[1, 0], [-1, 0], [0, 1], [0, -1]]

    q = deque([s])
    while q:
        c = q.popleft()
        for m in moves:
            my, mx = c[0] + m[0], c[1] + m[1]

            if f[my][mx] == ".":
                f[my][mx] = f[c[0]][c[1]] + 1
                q.append([my, mx])
                goal = [my, mx]
            else:
                continue

    return goal, f[goal[0]][goal[1]]


def main():
    H, W = map(int, input().split())
    field = []

    for h in range(H + 2):
        field.append(["#"] * (W + 2))
        if 1 <= h <= (H):
            field[h][1:-1] = list(map(str, input().rstrip()))

    ans = 0
    for y in range(1, H + 1):
        if "." in field[y]:
            start = [y, field[y].index(".")]
    goal, _ = bfs(start, copy.deepcopy(field))
    _, ans = bfs(goal, field)

    print(ans)


if __name__ == '__main__':
    main()