W, H = map(int, input().split())
maze = [input() for i in range(H)]
dist = [[W * H for j in range(W * H)] for j in range(W * H)]

for y in range(H):
    for x in range(W):
        dist[y * W + x][y * W + x] = 0
        for dy, dx in ((0, 1), (0, -1), (-1, 0), (1, 0)):
            if 0 <= y + dy < H and 0 <= x + dx < W:
                if maze[y + dy][x + dx] == '#':
                    dist[y * W + x][(y + dy) * W + (x + dx)] = 1
                else:
                    dist[y * W + x][(y + dy) * W + (x + dx)] = 0

for k in range(W * H):
    for i in range(W * H):
        for j in range(W * H):
            dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j])

min_cost = W * H
for y in range(H):
    for x in range(W):
        if maze[y][x] == '#':
            continue
        for i in range(y, H):
            for j in range(W):
                if maze[i][j] == '#':
                    continue
                if dist[y * W + x][i * W + j] > 0:
                    min_cost = min(min_cost, dist[y * W + x][i * W + j])
print(min_cost)