from collections import deque

from itertools import permutations

import sys

input = sys.stdin.readline

dx = [1, -1, 0, 0]

dy = [0, 0, 1, -1]

def bfs(x, y):

q = deque()

c = [[0]*w for _ in range(h)]

q.append([x, y])

c[x][y] = 1

while q:

x, y = q.popleft()

for i in range(4):

nx = x + dx[i]

ny = y + dy[i]

if 0 <= nx < h and 0 <= ny < w:

if a[nx][ny] != 'x' and not c[nx][ny]:

c[nx][ny] = c[x][y] + 1

q.append([nx, ny])

return c

while True:

w, h = map(int, input().split())

if not w and not h:

break

a, d = [], []

for i in range(h):

row = list(input().strip())

a.append(row)

for j, k in enumerate(row):

if k == 'o':

sx, sy = i, j

elif k == '*':

d.append([i, j])

r2d, flag = [], 0

c = bfs(sx, sy)

for i, j in d:

if not c[i][j]:

flag = 1

break

r2d.append(c[i][j]-1)

if flag:

print(-1)

continue

d2d = [[0]*len(d) for _ in range(len(d))]

for i in range(len(d)-1):

c = bfs(d[i][0], d[i][1])

for j in range(i+1, len(d)):

d2d[i][j] = c[d[j][0]][d[j][1]]-1

d2d[j][i] = d2d[i][j]

p = list(permutations([i for i in range(len(d2d))]))

ans = sys.maxsize

for i in p:

dist = 0

dist += r2d[i[0]]

nfrom = i[0]

for j in range(1, len(i)):

nto = i[j]

dist += d2d[nfrom][nto]

nfrom = nto

ans = min(ans, dist)

print(ans)