#include<iostream>
#include<queue>
#define inf 999999999
using namespace std;

struct node
{
	int x, y;
}dirty_point[15];

struct Node
{
	int x, y, step;
};

char map[25][25];
bool vis[25][25], dd[15];
int bb[15][15];// bfs
int dir[4][2] = {-1, 0, 1, 0, 0 , -1, 0, 1};
int w, h, minMove, flag;
queue<Node> qq; 

bool inmap(int x, int y)
{
	return (x >= 0 && x < h && y >= 0 && y < w && map[x][y] != 'x');
}

void dfs(int x, int sum, int count, int n)
{
	int i;
	if(count == n)
	{
		if(sum < minMove)
			minMove = sum;
		return ;
	}
	if(sum > minMove)	
		return ;
	for(i = 0; i < n; i++)
	{
		if(!dd[i] && bb[x][i] != 0 && x != i)
		{
			dd[i] = true;
			dfs(i, sum + bb[i][x], count + 1, n);
			dd[i] = false;
		}
	}
}

int bfs(int x, int y)
{
	int i, j, k;
	Node tmp, now;
	while(!qq.empty())
	{
		now = qq.front();
		qq.pop();
		for(k = 0; k < 4; k++)
		{
			i = now.x + dir[k][0];
			j = now.y + dir[k][1];
			if(!inmap(i, j) || vis[i][j])
				continue;
			if(i == dirty_point[y].x && j == dirty_point[y].y)
			{
				bb[x][y] = now.step + 1;
				bb[y][x] = now.step + 1;
				return now.step + 1;
			}
			tmp.x = i;
			tmp.y = j;
			tmp.step = now.step + 1;
			qq.push(tmp);
			vis[i][j] = true;
		}
	}
	return -1;
}

int main()
{
	int i, j;
	while(scanf("%d %d", &w, &h) == 2)
	{
		int n = 1;
		if(w == 0 && h == 0)
			break;
		memset(bb, 0, sizeof(bb));
		memset(dd, false, sizeof(dd));
		minMove = inf;
		for(i = 0; i < h; i++)
		{
			scanf("%s", &map[i]);
			for(j = 0; j < w; j++)
			{
				if(map[i][j] == 'o')
				{
					dirty_point[0].x = i;
					dirty_point[0].y = j;
				}
				if(map[i][j] == '*')
				{
					dirty_point[n].x = i;
					dirty_point[n++].y = j;
				}
			}
		}
		for(i = 0; i <= n-2; i++)
			for(j = i+1; j <= n-1; j++)
			{
				memset(vis, false, sizeof(vis));
				while(!qq.empty())
					qq.pop();
				Node tmp;
				tmp.x = dirty_point[i].x;
				tmp.y = dirty_point[i].y;
				tmp.step = 0;
				qq.push(tmp);
				vis[tmp.x][tmp.y] = true;
				flag = bfs(i,j);	
				if(flag == -1)
				{
					printf("-1\n");
					break;
				}
			}
		if(flag == -1)
			continue;
		dd[0] = true;
		dfs(0, 0, 1, n);
		printf("%d\n", minMove);
	}
	return 0;
}