// #define DEBUGGING
#include <bits/stdc++.h>
#define endl '\n'
#define ALL(V) (V).begin(), (V).end()
#define ALLR(V) (V).rbegin(), (V).rend()
using ll = std::int64_t;
using ull = std::uint64_t;
using PLL = std::pair<ll, ll>;
using TLL = std::tuple<ll, ll, ll>;
template <typename T> using V = std::vector<T>;
template <typename T> using VV = V<V<T>>;
template <typename T> const T& var_min(const T &t) { return t; }
template <typename T> const T& var_max(const T &t) { return t; }
template <typename T, typename... Tail> const T& var_min(const T &t, const Tail&... tail) { return std::min(t, var_min(tail...)); }
template <typename T, typename... Tail> const T& var_max(const T &t, const Tail&... tail) { return std::max(t, var_max(tail...)); }
template <typename T, typename... Tail> void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); }
template <typename T, typename... Tail> void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); }
template <typename T> const T& clamp(const T &t, const T &low, const T &high) { return std::max(low, std::min(high, t)); }
template <typename T> void chclamp(T &t, const T &low, const T &high) { return t = clamp(t, low, high); }
namespace init__ { struct InitIO { InitIO() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << std::fixed << std::setprecision(30); } } init_io; }
#define mv_rec make_v(init, tail...)
template <typename T> T make_v(T init) { return init; }
template <typename T, typename... Tail> auto make_v(T init, size_t s, Tail... tail) { return V<decltype(mv_rec)>(s, mv_rec); }
#undef mv_rec
using namespace std;

#ifdef DEBUGGING
#include "../../debug/debug.cpp"
#else
#define DEBUG(...) 0
#define DEBUG_SEPARATOR_LINE 0
#endif

const ll inf = 5e15;

tuple<VV<ll>, V<ll>, ll> grid2graph(const V<string> &grid, ll H, ll W) {
    auto graph = make_v<ll>(inf, H * W, H * W);
    V<ll> taint;
    ll robot;
    ll dh[] = { 1, 0, -1, 0, };
    ll dw[] = { 0, 1, 0, -1, };
    
    auto make_id = [&](ll h, ll w) { return h * W + w; };
    auto valid = [&](ll h, ll w) { return 0 <= h && h < H && 0 <= w && w < W; };

    for (ll h = 0; h < H; h++) for (ll w = 0; w < W; w++) {
        ll id = make_id(h, w);
        char c = grid[h][w];
        if (c == 'x') continue;
        if (c == 'o') robot = id;
        if (c == '*') taint.push_back(id);
        graph[id][id] = 0;
        for (ll i = 0; i < 4; i++) {
            ll nh = h + dh[i], nw = w + dw[i];
            if (!valid(nh, nw)) continue;
            if (grid[nh][nw] == 'x') continue;
            ll nid = make_id(nh, nw);
            graph[id][nid] = 1;
        }
    }

    return make_tuple(move(graph), move(taint), robot);
}

bool solve() {
    ll H, W;
    cin >> W >> H;
    if (!(H + W)) return false;
    V<string> grid(H);
    for (auto &&e : grid) cin >> e;
    VV<ll> dists;
    V<ll> taint;
    ll robot;
    tie(dists, taint, robot) = grid2graph(grid, H, W);
    for (ll k = 0; k < dists.size(); k++) for (ll i = 0; i < dists.size(); i++) for (ll j = 0; j < dists.size(); j++) chmin(dists[i][j], dists[i][k] + dists[k][j]);
    sort(ALL(taint));
    ll ans = inf;
    do {
        ll cur = robot, tmp = 0;
        for (ll t : taint) {
            tmp += dists[cur][t];
            cur = t;
        }
        chmin(ans, tmp);
    } while (next_permutation(ALL(taint)));
    cout << (inf <= ans ? -1 : ans) << endl;
    return true;
}

int main() {
    while (solve());
    return 0;
}



Measured memory_bytes: 3984