using System;
using System.Linq;
using System.Collections.Generic;
using Debug = System.Diagnostics.Debug;
using SB = System.Text.StringBuilder;
//using System.Numerics;
using Number = System.Int64;
//using static System.Math;
//using static MathEx;
//using P = System.Collections.Generic.KeyValuePair<int, int>;


namespace Program
{
    public class Solver
    {


        public void Solve()
        {
            for (;;)
            {
                var w = sc.Integer();
                var h = sc.Integer();
                if (w == 0) return;
                var mat = Enumerate(h, x => sc.Char(w));
                var n = w * h;
                var g = Enumerate(n, x => new int[n]);
                for (int i = 0; i < n; i++)
                    for (int j = i + 1; j < n; j++)
                    {
                        g[i][j] = g[j][i] = 100000000;
                    }
                var s = -1;
                int[] dx = { 1, 0, -1, 0 };
                int[] dy = { 0, 1, 0, -1 };
                var p = new List<int>();
                for (int i = 0; i < h; i++)
                    for (int j = 0; j < w; j++)
                    {
                        if (mat[i][j] == 'o') s = i * w + j;
                        if (mat[i][j] == '*') p.Add(i * w + j);
                        if (mat[i][j] == 'x') continue;
                        for (int k = 0; k < 4; k++)
                        {
                            var nx = i + dx[k];
                            var ny = j + dy[k];
                            if (nx < 0 || nx >= h || ny < 0 || ny >= w) continue;
                            if (mat[nx][ny] == 'x') continue;
                            g[i * w + j][nx * w + ny] = 1;
                        }
                    }
                for (int k = 0; k < n; k++)
                    for (int i = 0; i < n; i++)
                        for (int j = 0; j < n; j++)
                            g[i][j] = Math.Min(g[i][j], g[i][k] + g[k][j]);
                p.Add(s); p.Reverse();
                var m = p.Count;
                var gg = Enumerate(m, x => new int[m]);
                for (int i = 0; i < m; i++)
                    for (int j = 0; j < m; j++)
                        gg[i][j] = g[p[i]][p[j]];
                subsolve(gg);
            }
        }
        void subsolve(int[][] g)
        {
            var n = g.Length;
            var dp = Enumerate(1 << n, x => new int[n]);
            for (int i = 0; i < 1 << n; i++)
                for (int j = 0; j < n; j++)
                    dp[i][j] = 100000000;
            dp[1][0] = 0;
            for (int i = 0; i < 1 << n; i++)
                for (int j = 0; j < n; j++)
                {
                    if (dp[i][j] == 100000000) continue;
                    for (int k = 0; k < n; k++)
                        dp[i | 1 << k][k] = Math.Min(dp[i | 1 << k][k], dp[i][j] + g[j][k]);
                }
            var min = 100000000;
            for (int i = 0; i < n; i++)
                min = Math.Min(min, dp[(1 << n) - 1][i]);
            if (min == 100000000) min = -1;
            IO.Printer.Out.WriteLine(min);
        }
        /*
        int ri => sc.Integer();
        long rl => sc.Long();
        double rd => sc.Double();
        string rs => sc.Scan();
        char rc => sc.Char();

        [System.Diagnostics.Conditional("DEBUG")]
        void put(params object[] a) => Debug.WriteLine(string.Join(" ", a));

        //*/
        public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput());

        static T[] Enumerate<T>(int n, Func<int, T> f)
        {
            var a = new T[n];
            for (int i = 0; i < n; ++i) a[i] = f(i);
            return a;
        }
        static void Swap<T>(ref T a, ref T b)
        {
            var tmp = a;
            a = b;
            b = tmp;
        }
    }
}

#region main

static class Ex
{
    //public static string AsString(this IEnumerable<char> ie) { return new string(ie.ToArray()); }

    //public static string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ") { return string.Join(st, ie); }

    public static void Main()
    {
        var solver = new Program.Solver();
        solver.Solve();
        Program.IO.Printer.Out.Flush();
    }
}

#endregion
#region Ex

namespace Program.IO
{
    using System.IO;
    using System.Text;
    using System.Globalization;

    public class Printer: StreamWriter
    {
        static Printer()
        {
            Out = new Printer(Console.OpenStandardOutput()) { AutoFlush = false };
        }

        public static Printer Out { get; set; }

        public override IFormatProvider FormatProvider
        {
            get { return CultureInfo.InvariantCulture; }
        }

        public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true))
        {
        }

        public Printer(Stream stream, Encoding encoding) : base(stream, encoding)
        {
        }

        public void Write<T>(string format, T[] source)
        {
            base.Write(format, source.OfType<object>().ToArray());
        }

        public void WriteLine<T>(string format, T[] source)
        {
            base.WriteLine(format, source.OfType<object>().ToArray());
        }
    }

    public class StreamScanner
    {
        public StreamScanner(Stream stream)
        {
            str = stream;
        }

        public readonly Stream str;
        private readonly byte[] buf = new byte[1024];
        private int len, ptr;
        public bool isEof;

        public bool IsEndOfStream
        {
            get { return isEof; }
        }

        private byte read()
        {
            if (isEof) return 0;
            if (ptr < len) return buf[ptr++];
            ptr = 0;
            if ((len = str.Read(buf, 0, 1024)) > 0) return buf[ptr++];
            isEof = true;
            return 0;
        }

        public char Char()
        {
            byte b;
            do b = read(); while ((b < 33 || 126 < b) && !isEof);
            return (char)b;
        }

        public string Scan()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
                sb.Append(b);
            return sb.ToString();
        }

        public string ScanLine()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b != '\n'; b = (char)read())
                if (b == 0) break;
                else if (b != '\r') sb.Append(b);
            return sb.ToString();
        }

        public long Long()
        {
            if (isEof) return long.MinValue;
            long ret = 0;
            byte b;
            var ng = false;
            do b = read(); while (b != 0 && b != '-' && (b < '0' || '9' < b));
            if (b == 0) return long.MinValue;
            if (b == '-')
            {
                ng = true;
                b = read();
            }
            for (; ; b = read())
            {
                if (b < '0' || '9' < b)
                    return ng ? -ret : ret;
                ret = ret * 10 + b - '0';
            }
        }

        public int Integer()
        {
            return (isEof) ? int.MinValue : (int)Long();
        }

        public double Double()
        {
            var s = Scan();
            return s != "" ? double.Parse(s, CultureInfo.InvariantCulture) : double.NaN;
        }

        static T[] enumerate<T>(int n, Func<T> f)
        {
            var a = new T[n];
            for (int i = 0; i < n; ++i) a[i] = f();
            return a;
        }

        public char[] Char(int n)
        {
            return enumerate(n, Char);
        }

        public string[] Scan(int n)
        {
            return enumerate(n, Scan);
        }

        public double[] Double(int n)
        {
            return enumerate(n, Double);
        }

        public int[] Integer(int n)
        {
            return enumerate(n, Integer);
        }

        public long[] Long(int n)
        {
            return enumerate(n, Long);
        }
    }
}

#endregion


Measured memory_bytes: 11436