#include <bits/stdc++.h>

#define FOR(i,a,b) for(int i= (a); i<((int)b); ++i)
#define RFOR(i,a) for(int i=(a); i >= 0; --i)
#define FOE(i,a) for(auto i : a)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define DUMP(x)  cerr << #x << " = " << (x) << endl;
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v,x) (std::find(v.begin(), v.end(), x) != v.end())
#define BIT(n) (1LL<<(n))
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());

typedef long long LL;
template<typename T> using V = std::vector<T>;
template<typename T> using VV = std::vector<std::vector<T>>;
template<typename T> using VVV = std::vector<std::vector<std::vector<T>>>;

template<class T> inline T ceil(T a, T b) { return (a + b - 1) / b; }
template<class T> inline void print(T x) { std::cout << x << std::endl; }
template<class T> inline void print_vec(const std::vector<T> &v) { for (int i = 0; i < v.size(); ++i) {  if (i != 0) {std::cout << " ";} std::cout << v[i];} std::cout << "\n"; }
template<class T> inline bool inside(T y, T x, T H, T W) {return 0 <= y and y < H and 0 <= x and x < W; }
template<class T> inline double euclidean_distance(T y1, T x1, T y2, T x2) { return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)); }
template<class T> inline double manhattan_distance(T y1, T x1, T y2, T x2) { return abs(x1 - x2) + abs(y1 - y2); }

const int INF = 1L << 30;
const double EPS = 1e-9;
const std::string YES = "YES", Yes = "Yes", NO = "NO", No = "No";
const std::vector<int> dy4 = { 0, 1, 0, -1 }, dx4 = { 1, 0, -1, 0 };    // 4近傍（右, 下, 左, 上）
const std::vector<int> dy8 = { 0, -1, 0, 1, 1, -1, -1, 1 }, dx8 = { 1, 0, -1, 0, 1, 1, -1, -1 };

using namespace std;


map<pair<pair<int, int>,pair<int, int>>, LL> memo;
LL dist(pair<int, int> p1, pair<int, int> p2, const vector<string> &f) {
    auto key = make_pair(p1, p2);
    auto key2 = make_pair(p2, p1);
    if (memo.find(key) != memo.end()) {
        return memo[key];
    }
    if (memo.find(key2) != memo.end()) {
        return memo[key2];
    }

    vector<vector<LL>> cost(f.size(), vector<LL>(f[0].size(), INF));
    cost[p1.first][p1.second] = 0;

    queue<pair<int, int>> que;
    que.push(p1);

    while (not que.empty()) {
        int y = que.front().first;
        int x = que.front().second;
        que.pop();

        FOR(i, 0, 4) {
            int ny = dy4[i] + y;
            int nx = dx4[i] + x;

            if (inside(ny, nx, (int)f.size(), (int)f[0].size()) and f[ny][nx] != 'x' and cost[ny][nx] > cost[y][x] + 1) {
                cost[ny][nx] = cost[y][x] + 1;
                que.push(make_pair(ny, nx));
            }
        }
    }

    return memo[key] = cost[p2.first][p2.second];
}

int main() {
    cin.tie(0);
	ios::sync_with_stdio(false);

    while (true) {
        memo.clear();
        int W, H;
        cin >> W >> H;
        if (W == 0 and H == 0) {
            break;
        }

        vector<pair<int, int>> v;
        vector<string> f(H);
        int sy, sx;
        FOR(i, 0, H) {
            cin >> f[i];
            FOR(j, 0, W) {
                if (f[i][j] == 'o') {
                    sy = i;
                    sx = j;
                }
                if (f[i][j] == '*') {
                    v.emplace_back(make_pair(i, j));
                }
            }
        }

        if (v.size() == 0) {
            print(0);
            continue;
        }

        LL ans = INF;
        sort(ALL(v));
        do {
            LL d = dist(make_pair(sy, sx), v[0], f);
            FOR(i, 0, v.size() - 1) {
                d += dist(v[i], v[i + 1], f);
            }
            ans = min(ans, d);

        } while(next_permutation(ALL(v)));

        if (ans == INF) {
            print(-1);
        }
        else {
            print(ans);
        }

    }

	return 0;
}


Measured memory_bytes: 3136