#include <bits/stdc++.h>
                            #include<iostream>
                            #include<cstdio>
                            #include<vector>
                            #include<queue>
                            #include<map>
                            #include<cstring>
                            #include<string>
                            #include <math.h>
                            #include<algorithm>
                        //    #include <boost/multiprecision/cpp_int.hpp>
                            #include<functional>
                     #define int long long
                            #define inf  1000000007
                            #define pa pair<int,int>
                            #define ll long long
                            #define pal pair<double,pa>
                            #define ppa pair<pa,int>
                            #define ppap pair<int,pa>
                            #define ssa pair<string,int>
                            #define  mp make_pair
                            #define  pb push_back
                            #define EPS (1e-10)
                            #define equals(a,b) (fabs((a)-(b))<EPS)
                     
                            using namespace std;
                  
                            class Point{
                            	public:
                            	double x,y;
                            	Point(double x=0,double y=0):x(x),y(y) {}
                            	Point operator + (Point p) {return Point(x+p.x,y+p.y);}
                            	Point operator - (Point p) {return Point(x-p.x,y-p.y);}
                            	Point operator * (double a) {return Point(x*a,y*a);}
                            	Point operator / (double a) {return Point(x/a,y/a);}
                            	double absv() {return sqrt(norm());}
                            	double norm() {return x*x+y*y;}
                            	bool operator < (const Point &p) const{
                            		return x != p.x ? x<p.x: y<p.y;
                            	}
                            	bool operator == (const Point &p) const{
                            		return fabs(x-p.x)<EPS && fabs(y-p.y)<EPS;
                            	}
                            };
                            typedef Point Vector;
                     
                            struct Segment{
                            Point p1,p2;
                            };
                             double dot(Vector a,Vector b){
                            	return a.x*b.x+a.y*b.y;
                            }
                            double cross(Vector a,Vector b){
                            	return a.x*b.y-a.y*b.x;
                            }
                        
bool parareru(Point a,Point b,Point c,Point d){
//	if(abs(cross(a-b,d-c))<EPS)cout<<"dd "<<cross(a-b,d-c)<<endl;
	return abs(cross(a-b,d-c))<EPS;
}
double distance_ls_p(Point a, Point b, Point c) {
  if ( dot(b-a, c-a) < EPS ) return (c-a).absv();
  if ( dot(a-b, c-b) < EPS ) return (c-b).absv();
  return abs(cross(b-a, c-a)) / (b-a).absv();
}
bool is_intersected_ls(Segment a,Segment b) {
	if(parareru((a.p2),(a.p1),(a.p1),(b.p2))&&parareru((a.p2),(a.p1),(a.p1),(b.p1))){
//		cout<<"sss"<<endl;
		if(dot(a.p1-b.p1,a.p1-b.p2)<EPS) return true;
		if(dot(a.p2-b.p1,a.p2-b.p2)<EPS) return true;
		if(dot(a.p1-b.p1,a.p2-b.p1)<EPS) return true;
		if(dot(a.p1-b.p2,a.p2-b.p2)<EPS) return true;
		return false;
	}
  else return ( cross(a.p2-a.p1, b.p1-a.p1) * cross(a.p2-a.p1, b.p2-a.p1) < EPS ) && ( cross(b.p2-b.p1, a.p1-b.p1) * cross(b.p2-b.p1, a.p2-b.p1) < EPS );
}

double segment_dis(Segment a,Segment b){
	if(is_intersected_ls(a,b))return 0;
	double r=distance_ls_p(a.p1, a.p2, b.p1);
	r=min(r,distance_ls_p(a.p1, a.p2, b.p2));
	r=min(r,distance_ls_p(b.p1, b.p2, a.p2));
	r=min(r,distance_ls_p(b.p1, b.p2, a.p1));
	return r;
}


                string itos( int i ) {
                ostringstream s ;
                s << i ;
                return s.str() ;
                }
                 
                int gcd(int v,int b){
                	if(v>b) return gcd(b,v);
                	if(v==b) return b;
                	if(b%v==0) return v;
                	return gcd(v,b%v);
                }
 
                double distans(double x1,double y1,double x2,double y2){
                	double rr=(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
                	return sqrt(rr);
                	
                }
                /*}
int pr[100010];
//int inv[100010];
 
int beki(int wa,int rr){
	if(rr==0) return 1ll;
	if(rr==1) return wa;
	if(rr%2==1) return (beki(wa,rr-1)*wa)%inf;
	int zx=beki(wa,rr/2);
	return (zx*zx)%inf;
}
  
void gya(){
	pr[0]=1;
	for(int i=1;i<100010;i++){
		pr[i]=(pr[i-1]*i)%inf;
	}
	for(int i=0;i<100010;i++) inv[i]=beki(pr[i],inf-2);
	
}

*/

                         //----------------kokomade tenpure------------


int dx[4]={1,0,-1,0},dy[4]={0,-1,0,1};
int q[30][30];
int n,w,h;
vector<pa> ve;

int xs,ys;
bool b;
int dis(int x1,int y1,int x2,int y2){
	
	queue<ppap> st;
	int sumi[30][30]={0};
	st.push(mp(0,mp(x1,y1)));
	while((st.size())>0){
		ppap z=st.front();
		st.pop();
		if(z.second.first==x2 && z.second.second==y2) return z.first;
		if(sumi[z.second.first][z.second.second]==1) continue;
		sumi[z.second.first][z.second.second]=1;
		
		for(int i=0;i<4;i++){
			if(q[z.second.first+dx[i]][z.second.second+dy[i]]==0) st.push(mp(z.first+1,mp(z.second.first+dx[i],z.second.second+dy[i])));
		}	
		
		
	}
	b=false;
	return -1;
	
}


signed main(){

	int cnt=0;
	while(1){
		
		cin>>w>>h;
		if(w==0) return 0;
		ve.clear();
		for(int i=0;i<30;i++)for(int j=0;j<30;j++)q[i][j]=-1;
		
		for(int i=1;i<=h;i++){
			string s;
			cin>>s;
			for(int j=0;j<w;j++){
				if(s[j]!='x'){
					q[i][j+1]=0;
					if(s[j]=='*')ve.pb(mp(i,j+1));
					if(s[j]=='o') xs=i,ys=j+1;
				}
			}
		}
		
		int d[15][15];
		b=true;
		for(int i=0;i<ve.size();i++)for(int j=i+1;j<ve.size();j++){
			int g=dis(ve[i].first,ve[i].second,ve[j].first,ve[j].second);
			d[i+1][j+1]=g;
			d[j+1][i+1]=g;
		//	cout<<i<<" "<<j<<" "<<g<<endl;
		}
		for(int i=0;i<ve.size();i++){
			int g=dis(xs,ys,ve[i].first,ve[i].second);
			d[0][i+1]=g;
			d[i+1][0]=g;
		}
		
		if(!b){
			cout<<-1<<endl;
		}
		else{
		vector<int> a;
		for(int i=1;i<=ve.size();i++)a.pb(i);
		int ans=1000000000;
		do {
			int y=0;
			for(int i=0;i<a.size()-1;i++) y+= d[a[i]][a[i+1]];
			y += d[0][a[0]];
			ans=min(ans,y);
 			  
  		} while (next_permutation(a.begin(), a.end()));
			cout<<ans<<endl;
		}
	}
	
	
	return 0;
}

Measured memory_bytes: 3180