#include <iostream>
#include <string>
#include <utility>
#include <climits>
#include <set>
#include <vector>
#include <algorithm>

using namespace std;

const int DIR[] = {0, 1, 1,0,0,-1,-1,0};
const char KABE = 'x';

int
main()
{
  int width, height;
  int case_count = 0;
  while (cin >> width >> height && !(width
                                     == 0 && height == 0)){
    char table[30][30];
    for (int x = 0; x < 30; ++x){
      for (int y = 0; y < 30; ++y){
        table[x][y] = KABE;
      }
    }
    pair<int, int> target[20];
    int dirty_count = 0;
    for (int y = 0; y < height; ++y){
      string in;
      cin >> in;
      for (int x = 0; x < width; ++x){
        char c = in[x];
        table[x + 1][y + 1] = c;
        if (c == 'o'){
          target[0] = make_pair(x + 1, y + 1);
        } else if (c == '*'){
          target[++dirty_count] = make_pair(x + 1, y + 1);
        }
      }
    }
    int dist[20][20];
    for (int i = 0; i < 20; ++i){
      for (int j = 0; j < 20; ++j){
        dist[i][j] = INT_MAX;
      }
    }
    for (int index = 0; index < dirty_count + 1; ++index){
      int counter = 0;
      set<pair<int, int> > set_open;
      set_open.insert(target[index]);
      set<pair<int, int> > set_close;
      while (!set_open.empty()){
        set<pair<int, int> > set_next;
        for (set<pair<int, int> >::iterator it = set_open.begin(); it != set_open.end(); ++it){
          int x = it->first;
          int y = it->second;
          for (int to = 0; to < dirty_count + 1; ++to){
            if (target[to] == make_pair(x, y)){
              dist[index][to] = counter;
            }
          }
          set_close.insert(*it);
          for (int dir = 0; dir < 4; ++dir){
            int nx = x + DIR[dir * 2 + 0];
            int ny = y + DIR[dir * 2 + 1];
            if (table[nx][ny] != KABE && set_close.find(make_pair(nx, ny)) == set_close.end()){
              set_next.insert(make_pair(nx, ny));
            }
          }
        }
        ++counter;
        set_open = set_next;
      }
    }
    /*
    cout << "case : " << case_count + 1 << endl;
    for (int i = 0; i < dirty_count + 1; ++i){
      for (int j = 0; j < dirty_count + 1; ++j){
        cout << " " << dist[j][i];
      }
      cout << endl;
      ++case_count;
      }
    */
    bool error = false;
    for (int i = 0; i < dirty_count + 1; ++i){
      for (int j = 0; j < dirty_count + 1; ++j){
        if (dist[i][j] == INT_MAX){
          error = true;
        }
      }
      if (error){
        break;
      }
    }
    if (error){
      cout << -1 << endl;
      continue;
    }
    vector<int> per;
    for (int i = 0; i < dirty_count + 1; ++i){
      per.push_back(i);
    }
    int answer = INT_MAX;
    do {
      int temp = 0;
      for (int i = 0; i < dirty_count; ++i){
        temp += dist[per[i]][per[i + 1]];
      }
      if (answer > temp){
        answer = temp;
      }
    } while (next_permutation(per.begin() + 1, per.end()));
    cout << answer << endl;
  }

  return 0;
}