#include "bits/stdc++.h"

using namespace std;
#ifdef _DEBUG
#define _GLIBCXX_DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

#define int long long
#define ll long long
#define ll1 1ll
#define ONE 1ll
#define DBG 1
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define loop(n) rep(loop, (0), (n))
#define all(c) begin(c), end(c)
const int INF =
sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9) + 7;
const double PI = acos(-1);
const double EPS = 1e-9;
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
using pii = pair<int, int>;
// template<class T> ostream &operator<<(ostream &os,T &t){dump(t);return os;}
template <typename T, typename S>
istream &operator>>(istream &is, pair<T, S> &p) {
	is >> p.first >> p.second;
	return is;
}
template <typename T, typename S>
ostream &operator<<(ostream &os, pair<T, S> &p) {
	os << p.first << " " << p.second;
	return os;
}

template <typename T> void printvv(const vector<vector<T>> &v) {
	cerr << endl;
	rep(i, 0, v.size()) rep(j, 0, v[i].size()) {
		if (typeid(v[i][j]).name() == typeid(INF).name() and v[i][j] == INF) {
			cerr << "INF";
		}
		else
			cerr << v[i][j];
		cerr << (j == v[i].size() - 1 ? '\n' : ' ');
	}
	cerr << endl;
}
/*
typedef __int128_t Int;
std::ostream &operator<<(std::ostream &dest, __int128_t value) {
std::ostream::sentry s(dest);
  if (s) {
	__uint128_t tmp = value < 0 ? -value : value;
	char buffer[128];
	char *d = std::end(buffer);
	do {
	  --d;
	  *d = "0123456789"[tmp % 10];
	  tmp /= 10;
	} while (tmp != 0);
	if (value < 0) {
	  --d;
	  *d = '-';
	}
	int len = std::end(buffer) - d;
	if (dest.rdbuf()->sputn(d, len) != len) {
	  dest.setstate(std::ios_base::badbit);
	}
  }
  return dest;
}

__int128 parse(string &s) {
  __int128 ret = 0;
  for (int i = 0; i < s.length(); i++)
	if ('0' <= s[i] && s[i] <= '9')
	  ret = 10 * ret + s[i] - '0';
  return ret;
}
*/

#ifndef _DEBUG
#define printvv(...)
#endif
void YES(bool f) { cout << (f ? "YES" : "NO") << endl; }
void Yes(bool f) { cout << (f ? "Yes" : "No") << endl; }
template <class T> bool chmax(T &a, const T &b) {
	if (a < b) {
		a = b;
		return true;
	}
	return false;
}
template <class T> bool chmin(T &a, const T &b) {
	if (a > b) {
		a = b;
		return true;
	}
	return false;
}

signed main(signed argc, char *argv[]) {
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout << fixed << setprecision(12);

	int W, H; 
	while (cin >> W >> H, W&&H) {
		vector<string>v(H); rep(i, 0, H) { cin >> v[i]; }
		int dx[] = { 1, 0, -1, 0 }, dy[] = { 0, 1, 0, -1 };
		auto inrange = [&](int x, int y) { return 0 <= x and x < H and 0 <= y and y < W; };
		vector<vector<int>>cost(W*H, vector<int>(W*H, INF));
		vector<int>p;
		int s;
		rep(i, 0, H)rep(j, 0, W) {
			if (v[i][j] == 'x')continue;
			cost[i*W + j][i*W + j] = 0;
			if (v[i][j] == 'o')s = i * W + j;
			else if (v[i][j] == '*')p.eb(i*W + j);
			rep(k, 0, 4) {
				int x = i + dx[k], y = j + dy[k];
				if (not inrange(x, y))continue;
				if (v[x][y] != 'x') {
					cost[i*W + j][x*W + y] = 1;
				}
			}
		}
		rep(k, 0, cost.size())rep(i, 0, cost.size())rep(j, 0, cost.size())chmin(cost[i][j], cost[i][k] + cost[k][j]);
		p.eb(s);
		reverse(all(p));
		int n = p.size();
		vector<vector<int>>dp(1 << p.size(), vector<int>(p.size(), INF));
		dp[1][0] = 0;
		rep(mask, 1, 1 << n) {
			rep(i, 0, n) {
				rep(j, 0, n) {
					if ((mask >> j) & 1)continue;
					chmin(dp[mask ^ (1 << j)][j], dp[mask][i] + cost[p[i]][p[j]]);
				}
			}
		}
		int ans = *min_element(all(dp.back()));
		dump(ans);
		if (ans == INF)ans = -1;
		cout << ans << endl;
	}
	return 0;
}



Measured memory_bytes: 4224