#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 bool inside(T y, T x, T H, T W) {return 0 <= y and y < H and 0 <= x and x < W; }
inline double distance(double y1, double x1, double y2, double x2) { return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (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> dy = { 0, 1, 0, -1 }, dx = { 1, 0, -1, 0 };    // 4近傍（右, 下, 左, 上）

using namespace std;


int dist(const vector<string> &field, int sy, int sx, int gy, int gx) {
    VV<int> memo(field.size(), V<int>(field[0].size(), INT_MAX));
    memo[sy][sx] = 0;

    queue<pair<int, int>> que;
    que.push(make_pair(sy, sx));
    while (not que.empty()) {
        auto now = que.front(); que.pop();
        int now_cost = memo[now.first][now.second];

        FOR(i, 0, 4) {
            int ny = dy[i] + now.first;
            int nx = dx[i] + now.second;

            if (inside(ny, nx, (int)field.size(), (int)field[0].size()) and (field[ny][nx] != 'x')) {
                if (memo[ny][nx] > now_cost + 1) {
                    que.push(make_pair(ny, nx));
                    memo[ny][nx] = now_cost + 1;
                }
            }
        }
    }
    return memo[gy][gx];
}


void solve(vector<string> &field) {
    int sy = -1, sx = -1;
    vector<pair<int, int>> v;
    FOR(y, 0, field.size()) {
        FOR(x, 0, field[0].size()) {
            if (field[y][x] == 'o') {
                sy = y;
                sx = x;
            }
            if (field[y][x] == '*') {
                v.emplace_back(make_pair(y, x));
            }
        }
    }

    V<int> first_cost_table(v.size(), INT_MAX);
    VV<int> cost_table(v.size(), V<int>(v.size(), INT_MAX));
    FOR(i, 0, v.size()) {
        first_cost_table[i] = dist(field, sy, sx, v[i].first, v[i].second);
        if (first_cost_table[i] == INT_MAX) {
            print(-1);
            return;
        }
        FOR(j, i + 1, v.size()) {
            cost_table[i][j] = dist(field, v[i].first, v[i].second, v[j].first, v[j].second);
            cost_table[j][i] = cost_table[i][j];
            if (cost_table[i][j] == INT_MAX) {
                print(-1);
                return;
            }
        }
    }

    int ans = INT_MAX;
    vector<int> route(v.size());
    iota(ALL(route), 0);
    do {

        int total = first_cost_table[route[0]];
        FOR(i, 0, route.size() - 1) {
            total += cost_table[route[i]][route[i + 1]];
        }
        ans = min(ans, total);

    } while(next_permutation(ALL(route)));

    print(ans);
    
}

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

    while (true) {
        int W, H;
        cin >> W >> H;
        if (W == 0 or H == 0) {
            break;
        }
        vector<string> field;
        FOR(_, 0, H) {
            string s;
            cin >> s;
            field.push_back(s);
        }

        solve(field);
    }
    return 0;
}


Measured memory_bytes: 3280