#include <iostream>
#include <iomanip>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <algorithm>
#include <functional>
#include <utility>
#include <numeric>
#include <iterator>

using namespace std;

typedef long long LL;
typedef unsigned long long ULL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int,int> PII;
typedef istringstream ISS;
typedef ostringstream OSS;

#define REP( i, m, n ) for ( int i = (int)( m ); i < (int)( n ); ++i )
#define FOR( v, c ) for ( auto &v : c )

#define EACH( it, c ) for ( auto it = c.begin(); it != c.end(); ++it )
#define ALL( c ) (c).begin(), (c).end()
#define DRANGE( c, p ) (c).begin(), (c).begin() + p, (c).end()

#define PB( n ) push_back( n )
#define MP( a, b ) make_pair( ( a ), ( b ) )
#define EXIST( c, e ) ( (c).find( e ) != (c).end() )

#define fst first
#define snd second

#define DUMP( x ) cerr << #x << " = " << ( x ) << endl
#define DEBUG( x ) cerr << __FILE__ << ":" << __LINE__ << ": " << #x << " = " << ( x ) << endl

const int INF = INT_MAX / 2;
const int dx[] = { 1, 0, -1, 0 };
const int dy[] = { 0, 1, 0, -1 };

struct Solver
{
	const int H, W;
	VS Board;

	Solver( int h, int w ) : H( h ), W( w )
	{
		Board.resize( H );
		FOR( line, Board )
		{
			cin >> line;
		}

		return;
	}

	operator int ()
	{
		vector<PII> posX;
		REP( i, 0, H )
		{
			REP( j, 0, W )
			{
				if ( Board[i][j] == 'o' )
				{
					posX.PB( MP( i, j ) );
				}
			}
		}
		REP( i, 0, H )
		{
			REP( j, 0, W )
			{
				if ( Board[i][j] == '*' )
				{
					posX.PB( MP( i, j ) );
				}
			}
		}

		map<PII,int> posToIdx;
		REP( i, 0, posX.size() )
		{
			posToIdx[ posX[i] ] = i;
		}

		const int N = posX.size();
		VVI G( N, VI( N, INF ) );
		REP( i, 0, N )
		{
			G[i][i] = 0;
		}

		REP( i, 0, posX.size() )
		{
			map<PII,int> dists( bfs( Board, posX[i] ) );
			FOR( dist, dists )
			{
				G[ posToIdx[ posX[i] ] ][ posToIdx[ dist.fst ] ] = dist.snd;
			}
		}

		VVI dp( 1 << N, VI( N, INF ) );
		dp[1][0] = 0;

		REP( mask, 0, 1 << N )
		{
			REP( i, 0, N )
			{
				REP( j, 0, N )
				{
					dp[ mask | 1 << j ][j] = min( dp[ mask | 1 << j ][j], dp[ mask ][i] + G[i][j] );
				}
			}
		}

		int res = *min_element( ALL( dp[ ( 1 << N ) - 1 ] ) );
		return res == INF ? -1 : res;
	}

	map<PII,int> bfs( VS board, PII s )
	{
		VVI dist( H, VI( W, INF ) );
		dist[ s.fst ][ s.snd ] = 0;

		queue<PII> que;
		que.push( s );

		map<PII,int> res;
		while ( !que.empty() )
		{
			PII cur = que.front();
			que.pop();

			if ( board[ cur.fst ][ cur.snd ] == 'x' )
			{
				continue;
			}
			if ( board[ cur.fst ][ cur.snd ] == '*' )
			{
				res[ cur ] = dist[ cur.fst ][ cur.snd ];
			}

			board[ cur.fst ][ cur.snd ] = 'x';

			REP( d, 0, 4 )
			{
				PII next( cur );
				next.fst += dy[d];
				next.snd += dx[d];

				if ( !( 0 <= next.fst && next.fst < H && 0 <= next.snd && next.snd < W ) || board[ next.fst ][ next.snd ] == 'x' )
				{
					continue;
				}

				dist[ next.fst ][ next.snd ] = dist[ cur.fst ][ cur.snd ] + 1;
				que.push( next );
			}
		}

		return res;
	}
};

int main()
{
	cin.tie( 0 );
	ios::sync_with_stdio( false );

	while ( true )
	{
		int w, h;
		cin >> w >> h;

		if ( !( w | h ) )
		{
			break;
		}

		cout << Solver( h, w ) << endl;
	}

	return 0;
}

Measured memory_bytes: 1316