// URL: https://yukicoder.me/problems/no/157

import std.algorithm, std.array, std.bitmanip, std.container, std.conv, std.format,
       std.functional, std.math, std.range, std.traits, std.typecons, std.stdio, std.string;

version(unittest) {} else
void main()
{
  int W, H; io.getV(W, H);
  string[] C; io.getC(H, C);

  alias rg = Region!(H, W), Pos = rg.Pos;
  auto c = rg.grid(cast(char[][])C), b = rg.grid!bool;

  auto findSpace()
  {
    foreach (p; rg.allPos)
      if (c[p] == '.' && !b[p]) {
        auto r = [p];
        b[p] = true;
        auto q = DList!(Pos)(p);
        while (!q.empty) {
          auto u = q.front; q.removeFront();
          foreach (v; u.around4) {
            if (c[v] == '.' && !b[v]) {
              r ~= v;
              b[v] = true;
              q.insertBack(v);
            }
          }
        }
        return r;
      }
    assert(0);
  }

  auto distManhattan(Pos p1, Pos p2) { return abs(p1.r-p2.r)+abs(p1.c-p2.c); }

  auto s1 = findSpace(), s2 = findSpace(), r = 1000;
  foreach (p1; s1)
    foreach (p2; s2)
      r = min(r, distManhattan(p1, p2));

  io.put(r-1);
}

template Region(alias h, alias w)
{
  struct Pos
  {
    pure nothrow @nogc @safe
    {
      int r, c;
      this(int r, int c)
      {
        this.r = r; this.c = c;
      }
      bool inRegion() const
      {
        return 0 <= r && r < h && 0 <= c && c < w;
      }
      int p2i() const
      {
        return cast(int)w*r+c;
      }

      Pos opBinary(string op)(Pos q) const
        if (op == "+" || op == "-")
      {
        return mixin("Pos(r"~op~"q.r, c"~op~"q.c)");
      }
      ref Pos opOpAssign(string op)(Pos q)
        if (op == "+" || op == "-")
      {
        mixin("r"~op~"=q.r; c"~op~"=q.c;");
        return this;
      }
      Pos opBinary(string op, U)(U a) const
        if ((op == "*" || op == "/") && isIntegral!U)
      {
        return mixin("Pos(r"~op~"a, c"~op~"a)");
      }
      ref Pos opOpAssign(string op, U)(U a)
        if ((op == "*" || op == "/") && isIntegral!U)
      {
        mixin("r"~op~"=a; c"~op~"=a;");
        return this;
      }
      int opBinary(string op: "*")(Pos q) const
      {
        return r*q.r+c*q.c;
      }
    }

    pure nothrow @safe
    {
      auto around4() const
      {
        return [Pos(r-1, c), Pos(r, c+1), Pos(r+1, c), Pos(r, c-1)]
          .filter!(p => p.inRegion);
      }
      auto around8() const
      {
        return [Pos(r-1, c), Pos(r-1, c+1), Pos(r, c+1), Pos(r+1, c+1),
                Pos(r+1, c), Pos(r+1, c-1), Pos(r, c-1), Pos(r-1, c-1)]
          .filter!(p => p.inRegion);
      }
    }
  }

  pure nothrow @safe
  {
    auto allPos()
    {
      return AllPosRange();
    }
  }

  private
  {
    struct AllPosRange
    {
      int r, c;
      @property pure Pos front() { return Pos(r, c); }
      void popFront() { if (++c >= w) { c = 0; ++r; } }
      pure bool empty() const { return r >= h; }
    }
  }

  struct Grid(T)
  {
    T[][] data;

    pure nothrow @safe
    {
      Grid!T dup() const
      {
        return Grid!T(data.map!"a.dup".array);
      }
    }

    pure nothrow @nogc @safe
    {
      this(T[][] data)
      {
        this.data = data;
      }

      T opIndex(size_t r, size_t c) const
        in { assert(0 <= r && r < h && 0 <= c && c < w); }
      do
      {
        return data[r][c];
      }
      T opIndex(Pos p) const
        in { assert(p.inRegion); }
      do
      {
        return data[p.r][p.c];
      }
      Grid!T opIndexAssign(T v, size_t r, size_t c)
        in { assert(0 <= r && r < h && 0 <= c && c < w); }
      do
      {
        data[r][c] = v;
        return this;
      }
      Grid!T opIndexAssign(T v, Pos p)
        in { assert(p.inRegion); }
      do
      {
        data[p.r][p.c] = v;
        return this;
      }
      Grid!T opIndexOpAssign(string op)(T v, size_t r, size_t c)
        in { assert(0 <= r && r < h && 0 <= c && c < w); }
      do
      {
        mixin("data[r][c]"~op~"=v;");
        return this;
      }
      Grid!T opIndexOpAssign(string op)(T v, Pos p)
        in { assert(p.inRegion); }
      do
      {
        mixin("data[p.r][p.c]"~op~"=v;");
        return this;
      }
      Grid!T opIndexUnary(string op)(size_t r, size_t c)
        if (op == "++" || op == "--")
        in { assert(0 <= r && r < h && 0 <= c && c < w); }
      do
      {
        mixin(op~"data[r][c];"); return this; }
      Grid!T opIndexUnary(string op)(Pos p)
        if (op == "++" || op == "--")
        in { assert(p.inRegion); }
      do
      {
        mixin(op~"data[p.r][p.c];");
        return this;
      }
    }
  }
  pure nothrow @safe
  {
    auto grid(T)(T[][] data = new T[][](h, w))
    {
      return Grid!T(data);
    }
  }
}

auto io = IO!()();
import std.stdio;
struct IO(alias IN = stdin, alias OUT = stdout)
{
  import std.meta : allSatisfy;
  import core.stdc.stdlib : exit;

  void getV(T...)(ref T v)
  {
    foreach (ref w; v) get(w);
  }
  void getA(T)(size_t n, ref T v)
    if (hasAssignableElements!T)
  {
    v = new T(n);
    foreach (ref w; v) get(w);
  }
  void getC(T...)(size_t n, ref T v)
    if (allSatisfy!(hasAssignableElements, T))
  {
    foreach (ref w; v) w = new typeof(w)(n);
    foreach (i; 0..n) foreach (ref w; v) get(w[i]);
  }
  void getM(T)(size_t r, size_t c, ref T v)
    if (hasAssignableElements!T && hasAssignableElements!(ElementType!T))
  {
    v = new T(r);
    foreach (ref w; v) getA(c, w);
  }
  template getS(E...)
  {
    void getS(T)(size_t n, ref T v)
    {
      v = new T(n);
      foreach (ref w; v) foreach (e; E) mixin("get(w."~e~");");
    }
  }

  const struct PutConf
  {
    bool newline = true, flush, exit;
    string floatFormat = "%.10f", delimiter = " ";
  }

  void put(alias conf = "{}", T...)(T v)
  {
    mixin("const PutConf c = "~conf~"; putMain!c(v);");
  }
  void putB(alias conf = "{}", S, T)(bool c, S t, T f)
  {
    if (c) put!conf(t);
    else put!conf(f);
  }
  void putRaw(T...)(T v)
  {
    OUT.write(v);
    OUT.writeln;
  }

  private
  {
    dchar[] buf;
    auto sp = (new dchar[](0)).splitter;

    void nextLine()
    {
      IN.readln(buf);
      sp = buf.splitter;
    }
    void get(T)(ref T v)
    {
      if (sp.empty) nextLine();
      v = sp.front.to!T;
      sp.popFront();
    }

    void putMain(PutConf c, T...)(T v)
    {
      foreach (i, w; v) {
        putOne!c(w);
        if (i+1 < v.length) OUT.write(c.delimiter);
      }
      static if (c.newline) OUT.writeln;
      static if (c.flush) OUT.flush();
      static if (c.exit) exit(0);
    }
    void putOne(PutConf c, T)(T v)
    {
      static if (isInputRange!T && !isSomeString!T) putRange!c(v);
      else static if (isFloatingPoint!T) OUT.write(format(c.floatFormat, v));
      else static if (hasMember!(T, "fprint")) v.fprint(OUT);
      else OUT.write(v);
    }
    void putRange(PutConf c, T)(T v)
    {
      auto w = v;
      while (!w.empty) {
        putOne!c(w.front); w.popFront();
        if (!w.empty) OUT.write(c.delimiter);
      }
    }
  }
}