#include <iostream>

 #include <cstdio>

 #include <algorithm>

 #include <cstring>

 #include <cmath>

 #include <string>

 #include <queue>

 #include <vector>

 #include <map>

 #include <set>

 using namespace std;

 #define pb(x) push_back(x)

 #define ll long long

 #define mk(x, y) make_pair(x, y)

 #define mem(a) memset(a, 0, sizeof(a))

 #define lson l, m, rt<<1

 #define rson m+1, r, rt<<1|1

 #define mem1(a) memset(a, -1, sizeof(a))

 #define mem2(a) memset(a, 0x3f, sizeof(a))

 #define rep(i, a, n) for(int i = a; i<n; i++)

 #define ull unsigned long long

 typedef pair<int, int> pll;

 const double PI = acos(-1.0);

 const int inf = ;

 const double eps = 1e-;

 const int mod = 1e9+;

 const int dir[][] = { {-, }, {, }, {, -}, {, } };

 char c[][];

 int dis[][], vis[][], n, m, cnt, ans, used[];

 struct node

 {

     int x, y, step;

     node(){}

     node(int x, int y, int step):x(x), y(y), step(step){}

 };

 int bfs(pll s, pll e) {

     mem(vis);

     vis[s.first][s.second] = ;

     queue <node> q;

     q.push(node(s.first, s.second, ));

     while(!q.empty()) {

         node tmp = q.front(); q.pop();

         if(tmp.x == e.first && tmp.y == e.second)

             return tmp.step;

         for(int i = ; i<; i++) {

             int tmpx = tmp.x + dir[i][];

             int tmpy = tmp.y + dir[i][];

             if(tmpx>=&&tmpx<n&&tmpy>=&&tmpy<m&&!vis[tmpx][tmpy]&&c[tmpx][tmpy]!='x') {

                 q.push(node(tmpx, tmpy, tmp.step+));

                 vis[tmpx][tmpy] = ;

             }

         }

     }

     return ;

 }

 void dfs(int now, int num, int now_dis) {

     if(now_dis>=ans)

         return ;

     if(num == cnt-) {

         if(now_dis<ans) {

             ans = now_dis;

         }

         return ;

     }

     for(int i = ; i<cnt; i++) {

         if(!used[i]) {

             used[i] = ;

             dfs(i, num+, now_dis+dis[now][i]);

             used[i] = ;

         }

     }

 }

 pll point[];

 int main()

 {

     while(scanf("%d%d", &m, &n)) {

         if(n+m==)

             break;

         int sx, sy;

         mem(dis);

         cnt = ;

         for(int i = ; i<n; i++)

             scanf("%s", c[i]);

         for(int i = ; i<n; i++) {

             for(int j = ; j<m; j++) {

                 if(c[i][j] == 'o') {

                     c[i][j] = '';

                     point[].first = i;

                     point[].second = j;

                 }

                 if(c[i][j] == '*') {

                     point[cnt].first = i;

                     point[cnt++].second = j;

                 }

             }

         }

         for(int i = ; i<cnt; i++) {

             for(int j = i+; j<cnt; j++) {

                 dis[i][j] = dis[j][i] = bfs(point[i], point[j]);

             }

         }

         int flag = ;

         for(int i = ; i<cnt; i++) {

             if(dis[][i] == ) {

                 flag = ;

             }

         }

         if(flag) {

             puts("-1");

             continue;

         }

         mem(used);

         used[] = ;

         ans = inf;

         dfs(, , );

         printf("%d\n", ans);

     }

 }