CLEANRBT

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
#define VI vector<int>
#define _f front
#define _b back
#define _pb push_back
#define _pf push_front
#define _Pb pop_back
#define _Pf pop_front
#define _all(v) v.begin(), v.end()
#define II pair<int,int>
#define III pair<int, II>
#define F first
#define S second
#define _mp make_pair
#define LINE  putc('\n', stdout)
#define SPACE putc(' ' , stdout)
#define TAB   putc('\t', stdout)
#define _out(_)            printf("%i",_)
#define __out(_,__)        printf("%i %i",_,__)
#define ___out(_,__,___)   printf("%i %i %i",_,__,___)
#define _outLL(_)          printf("%I64d",_)
#define __outLL(_,__)      printf("%I64d %I64d",_,__)
#define ___outLL(_,__,___) printf("%I64d %I64d %I64d",_,__,___)
#define _in(_)             scanf("%i", &_)
#define __in(_,__)         scanf("%i%i",&_,&__)
#define ___in(_,__,___)    scanf("%i%i%i",&_,&__,&___)
#define _inLL(_)           scanf("%I64d", &_)
#define __inLL(_,__)       scanf("%I64d%I64d",&_,&__)
#define ___inLL(_,__,___)  scanf("%I64d%I64d%I64d",&_,&__,&___)
#define _debug(_) printf("-----------> Debuging : %i\n",_ );
#define _for(i, n) for(int i=0 ; i<n ; i++)
#define _rof(i, n) for(int i=n ; i-- ;    )
#define rm_imp(d, p) (round(d*p)/p)
#define INF 2e8
char A[33*33];
VI v;
int w, h, n, dist[14][14], D[33*33];
int memo[14][1<<14];
int TSP(int p, int mask)
{
  if(mask==(1<<n)-1)    return 0;
  if(memo[p][mask]!=-1) return memo[p][mask];
  int ans = INF;
  _rof(i, n)
    if(!(mask&1<<i))
      ans= min(ans, TSP(i, mask|1<<i) + dist[p][i]);
  return memo[p][mask]=ans;
}
int generate_D(int source) //BFS search
{
  //           L   U   R    D
  int dir[] = {-1, w, +1 , -w};
  deque<int> dq;
  memset(D, -1, sizeof D);
  D[source]=0;
  dq._pf(source);//push_back
  while(!dq.empty())
  {
    int s = dq._f(); //front
    dq._Pf();//Pop-back
    _for(j, 4) //4 possible directions
    {
      int d = s + dir[j] ;
      if(D[d]==-1 && A[d]!='x') //not visited yet & not obstacle
        D[d]=D[s]+1 , dq._pb(d); //push_back
    }
  }
}
int main()
{
  repeate :
  while(__in(w,h), w)
  {
    memset(memo, -1, sizeof memo);
    v.clear(); //clear previous dirts + robot positions
    char *ptr = A;
    _for(i, w+2) *ptr++='x'; // make an upper bound of obstacles
    _for(i, h) { *ptr++='x'; scanf("%s", ptr); ptr+=w; *ptr++='x'; } //make left and right bound of obstacles
    _for(i, w+2) *ptr++='x'; // make a lower bound of obstacles
    *ptr=0; // end the string
    w+=2; h+=2; //update dementions
    v._pb(strstr(A, "o")-A); //search for robot position
    ptr=A; ptr--;
    while(ptr=strstr(ptr+1, "*")) v._pb(ptr-A); //search for dirts positions
    n = v.size();
    _for(i, n){
      generate_D(v[i]); //generate all distents from the source (v[i])
      _for(j, n){
        if(D[v[j]]==-1) {_out(-1);LINE;goto repeate;} //if a dirst is unreachable
        dist[i][j]=D[v[j]]; //add the sorest path to dist
      }
    }
    _out(TSP(0, 1));LINE; //dp with bitmasking
  }
}