#include<iostream>#include<cstring>using namespace std;//bfschar map[30][30];int m,n,pmap[30][30];int dt;int Sx,Sy;int d[4][2]={{1,0},{-1,0},{0,1},{0,-1}};//dfsint Dtx[15],Dty[15];int l[15][15]; bool visit[15];int pace,p; void dfs(int i,int sum){int j,min=0x3f3f3f,TEMP;if(pace==dt){p=sum;return;}visit[i]=1;for(j=1;j<=dt;j++){if(!visit[j]){pace++;if(sum+l[i][j]<=p)dfs(j,sum+l[i][j]);pace--;}}visit[i]=0;}struct Node{int x,y;};int bfs(int I,int J){int t=0,h=1,i;Node Q[1000];Q[t].x=Dtx[I];Q[t].y=Dty[I];while(t<h){Node T=Q[t];t++;if(map[T.y][T.x]=='x')continue;if(T.y==Dty[J]&&T.x==Dtx[J])return pmap[T.y][T.x];for(i=0;i<4;i++){int dx,dy;dx=T.x+d[i][1];dy=T.y+d[i][0];if(dx>=0&&dx<m&&dy>=0&&dy<n){Node &H=Q[h];H.x=dx;H.y=dy;if(pmap[H.y][H.x]==0){pmap[H.y][H.x]=pmap[T.y][T.x]+1;h++;}}}}return -1;}int main(){int i,j;while(cin>>m>>n&&(m||n)) {memset(map,0,sizeof(map));dt=0;for(i=0;i<n;i++){for(j=0;j<m;j++){cin>>map[i][j];if(map[i][j]=='o'){Dtx[0]=Sx=j;Dty[0]=Sy=i;}if(map[i][j]=='*'){dt++;Dtx[dt]=j;Dty[dt]=i;}}}p=1234567890;for(i=0;i<=dt;i++){for(j=i+1;j<=dt;j++){memset(pmap,0,sizeof(pmap));l[i][j]=bfs(i,j);if(l[i][j]==-1) {p=-1;break;}}if(p==-1)break;}if(p==-1)cout<<p<<endl;else{for(i=0;i<=dt;i++){for(j=i;j>=0;j--){l[i][j]=l[j][i];}}pace=0;memset(visit,0,sizeof(visit));dfs(0,0); cout<<p<<endl;}} return 0;}
