import java.util.Scanner;

public class CleaningRobot {
	static int M, N;
	static char map[][];
	static int result;
	static int[] dirtyX;
	static int[] dirtyY;
	static int numOfDirty;
	static int[][] director = { { 0, 1 }, { 1, 0 }, { 0, -1 }, { -1, 0 } };
	static int distance[][];
	static boolean impossible;

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		while (true) {
			N = in.nextInt();
			M = in.nextInt();
			if (M == 0 && N == 0)
				break;
			result = 0xfffff;
			impossible = false;
			dirtyX = new int[11];
			dirtyY = new int[11];
			numOfDirty = 0;
			map = new char[M][N];
			for (int i = 0; i < M; i++) {
				String s = in.next();
				for (int j = 0; j < N; j++) {
					map[i][j] = s.charAt(j);
					if (map[i][j] == '*') {
						numOfDirty++;
						dirtyX[numOfDirty] = i;
						dirtyY[numOfDirty] = j;
					} else if (map[i][j] == 'o') {
						dirtyX[0] = i;
						dirtyY[0] = j;
					}
				}
			}
			distance = new int[numOfDirty+1][numOfDirty+1];
			for(int i = 0; i < numOfDirty+1; i++){
				if(impossible)
					break;
				for(int j = i + 1; j < numOfDirty+1; j++){
					if(impossible)
						break;
					BFS(i, j);
				}
			}
			if(impossible){
				System.out.println(-1);
				continue;
			}
			DFS(0, 0, 0, new boolean[numOfDirty + 1]);
			System.out.println(result);
		}
		in.close();
	}
	
	static void BFS(int i, int j){
		int step = 0;
		boolean visited[][] = new boolean[M][N];
		int numInQue = 1;
		int queX[] = new int[M * N];
		int queY[] = new int[M * N];
		queX[0] = dirtyX[i];
		queY[0] = dirtyY[i];
		int destiX = dirtyX[j];
		int destiY = dirtyY[j];
		boolean flag = false;
		while(numInQue != 0){
			step++;
			int queXTEMP[] = new int[M * N];
			int queYTEMP[] = new int[M * N];
			int numInQueTemp = 0;
			for(int k = 0; k < numInQue; k++){
				for(int d = 0; d < 4; d++){
					int x = queX[k] + director[d][0];
					int y = queY[k] + director[d][1];
					if(x == destiX && y == destiY)
						flag = true;
					if(x >= 0 && x < M && y >= 0 && y < N && !visited[x][y] && map[x][y] != 'x'){
						queXTEMP[numInQueTemp] = x;
						queYTEMP[numInQueTemp] = y;
						numInQueTemp++;
						visited[x][y] = true;
					}
				}
			}
			if(flag)
				break;
			numInQue = numInQueTemp;
			queX = queXTEMP;
			queY = queYTEMP;
		}
		if(!flag){
			impossible = true;
			return;
		}
		distance[i][j] = step;
		distance[j][i] = step;
	}
	
	static void DFS(int step, int next, int preDis, boolean visited[]){
		if(preDis > result)
			return;
		if(step == numOfDirty){
			result = preDis;
			return;
		}
		for(int i = 1; i < numOfDirty + 1; i++){
			if(visited[i])
				continue;
			visited[i] = true;
			DFS(step + 1, i, preDis + distance[next][i], visited);
			visited[i] = false;
		}
	}
}