w, h = [ int(v) for v in input().split() ]

cave = [ list(input()) for i in range(h) ]
path_list = []

for i in range(h):
    for j in range(w):
        if cave[i][j] == ".":
            path_list.append((i,j))
            


def search():
    global path_list
    outlist = [path_list[0]]
    que = [path_list[0]]

    while que != []:
        y, x = que[0][0], que[0][1]
        if (y, x+1) in path_list and (y, x+1) not in outlist:
            outlist.append((y, x+1))
            que.append((y, x+1))
        if (y, x-1) in path_list and (y, x-1) not in outlist:
            outlist.append((y, x-1))
            que.append((y, x-1))
        if (y+1, x) in path_list and (y+1, x) not in outlist:
            outlist.append((y+1, x))
            que.append((y+1, x))
        if (y-1, x) in path_list and (y-1, x) not in outlist:
            outlist.append((y-1, x))
            que.append((y-1, x))
        del que[0]

    return outlist

path1 = sorted(search())
path2 = sorted([ i for i in path_list if i not in path1 ])

d = w*h

for i in path1:
    for j in path2:
        dij = abs(i[0]-j[0]) + abs(i[1]-j[1])

        d = min(dij,d)
print(d-1)