/* 22:21 - 23:37 */
#include <stdio.h>
#include <limits.h>

#define INFTY 10000

typedef struct { int x, y; } point_t; point_t p[16];

char map[22][23];
int adj[16][16];
int w, h, n;

int min;

int input()
{
  char s[1024];
  int i, j;

  gets(s); sscanf(s, "%d%d", &w, &h);
  if (w == 0 && h == 0) { return 0; }
  for (i = 0; i < w+2; i++) {
    map[0][i] = map[h+1][i] = 'x';
  }
  map[0][w+2] = map[h+1][w+2] = '\0';
  for (i = 1; i <= h; i++) {
    gets(&map[i][1]); map[i][0] = map[i][w+1] = 'x'; map[i][w+2] = '\0';
  }
  w += 2; h += 2;

  n = 0;
  for (i = 0; i < h; i++) {
    for (j = 0; j < w; j++) {
      if (map[i][j] == 'o' || map[i][j] == '*') { n++; }
    }
  }

  return 1;
}

int flood(int x, int y)
{
  int i, j, k, d, dist[22][22], found, pointdist[16];
  static int dx[4] = {0, 1, 0, -1};
  static int dy[4] = {1, 0, -1, 0};

  for (i = 0; i < h; i++) {
    for (j = 0; j < w; j++) {
      dist[i][j] = INFTY;
    }
  }
  for (i = 0; i < n; i++) { pointdist[i] = INFTY; }
  dist[y][x] = 0;
  pointdist[map[y][x]] = 0;

  /* Poor Version BFS */
  for (d = 0; ; d++) {
    found = 0;
    for (i = 1; i < h-1; i++) {
      for (j = 1; j < w-1; j++) {
        if (dist[i][j] == d) {
          for (k = 0; k < 4; k++) {
            if (map[i+dy[k]][j+dx[k]] != 'x' && dist[i+dy[k]][j+dx[k]] > dist[i][j]) {
              found = 1;
              dist[i+dy[k]][j+dx[k]] = d+1;
              if (0 <= map[i+dy[k]][j+dx[k]] && map[i+dy[k]][j+dx[k]] <= 15) {
                pointdist[map[i+dy[k]][j+dx[k]]] = d+1;
              }
            }
          }
        }
      }
    }
    if (!found) { break; }
  }

  for (i = 0; i < n; i++) {
    adj[map[y][x]][i] = adj[i][map[y][x]] = pointdist[i];
  }
  return 0;
}

int tsp(int visited[16], int cur, int sum)
{
  int i, found = 0;
  for (i = 0; i < n; i++) {
    if (!visited[i]) {
      found = 1;
      visited[i] = 1;
      tsp(visited, i, sum + adj[cur][i]);
      visited[i] = 0;
    }
  }
  if (!found) {
    if (min > sum) { min = sum; }
  }
}

int main()
{
  int i, j, visited[16], k;

  while (1) {
    if (!input()) { break; }

    for (i = 0; i < 16; i++) {
      for (j = 0; j < 16; j++) {
        adj[i][j] = INFTY;
      }
    }
    for (i = k = 0; i < h; i++) {
      for (j = 0; j < w; j++) {
        if (map[i][j] == 'o') { map[i][j] = 0; p[0].x = j; p[0].y = i; flood(j, i); }
        else if (map[i][j] == '*') { k++; map[i][j] = k; p[k].x = j; p[k].y = i; flood(j, i); }
      }
    }
    for (i = 0; i < n; i++) {
      for (j = 0; j < n; j++) {
        if (adj[i][j] >= INFTY) { printf("-1\n"); goto quit; }
      }
    }

    min = 100000;
    for (i = 1; i < n; i++) {
      visited[i] = 0;
    } visited[0] = 1;
    tsp(visited, 0, 0);
    printf("%d\n", min);
quit:
    continue;
  }
  return 0;
}