#include <bits/stdc++.h>
#define EPS 1e-9
#define INF 1070000000LL
#define MOD 1000000007LL
#define fir first
#define foreach(it,X) for(auto it=(X).begin();it!=(X).end();it++)
#define numa(x,a) for(auto x: a)
#define ite iterator
#define mp make_pair
#define rep(i,n) rep2(i,0,n)
#define rep2(i,m,n) for(int i=m;i<(n);i++)
#define pb push_back
#define pf push_front
#define sec second
#define sz(x) ((int)(x).size())
#define ALL( c ) (c).begin(), (c).end()
#define gcd(a,b) __gcd(a,b)
#define mem(x,n) memset(x,n,sizeof(x))
#define endl "\n"
using namespace std;
template <int POS, class TUPLE> void deploy(std::ostream &os, const TUPLE &tuple){}
template <int POS, class TUPLE, class H, class ...Ts> void deploy(std::ostream &os, const TUPLE &t){ os << (POS == 0 ? "" : ", ") << get<POS>(t); deploy<POS + 1, TUPLE, Ts...>(os, t); }
template <class T,class U> std::ostream& operator<<(std::ostream &os, std::pair<T,U> &p){ os << "(" << p.first <<", " << p.second <<")";return os; }
template <class T> std::ostream& operator<<(std::ostream &os, std::vector<T> &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; }
template <class T> std::ostream& operator<<(std::ostream &os, std::set<T> &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; }
template <class T, class K> std::ostream& operator<<(std::ostream &os, std::map<T, K> &mp){ int remain = mp.size(); os << "{"; for(auto e: mp) os << "(" << e.first << " -> " << e.second << ")" << (--remain == 0 ? "}" : ", "); return os; }
#define DEBUG1(var0) { std::cerr << (#var0) << "=" << (var0) << endl; }
#define DEBUG2(var0, var1) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG1(var1); }
#define DEBUG3(var0, var1, var2) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG2(var1,var2); }
#define DEBUG4(var0, var1, var2, var3) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG3(var1,var2,var3); }
using ll = long long;
int W,H;
int memo[30][30];
string board[30];
int group[30][30];
int dx[] = {-1,0,0,1};
int dy[] = {0,-1,1,0};
using PII = pair <pair <int,int>,int>;
inline bool in(int x,int y){
  return 0 <= x && x < H && 0 <= y && y < W;
}
void dfs(int x,int y, int g){
  if (board[x][y] == '#' || group[x][y] != 0) {
    return;
  }
  group[x][y] = g;
  rep(i,4){
    if (in(x+dx[i],y+dy[i])) {
      dfs(x+dx[i],y+dy[i],g);
    }
  }
}

int search(int x_,int y_,int x2, int y2){
  mem(memo,-1);
  priority_queue <PII,vector <PII>,greater<PII> > que;
  que.push(mp(mp(x_,y_),0));
  int now_cost = INF;
  while(!que.empty()){
    auto t = que.top();
    que.pop();
    auto x = t.fir.fir;
    auto y = t.fir.sec;
    auto c = t.sec;
    if (memo[x][y] >= 0 && memo[x][y] <= c) {
      continue;
    }
    if (now_cost <= c) {
      continue;
    }
    memo[x][y] = c;
    if (x == x2 && y == y2) {
      now_cost = min(now_cost,c);
      continue;
    }
    rep(i,4){
      if (in(x+dx[i],y+dy[i])) {
        auto c2 = c + (board[x+dx[i]][y+dy[i]] == '#');
        if (now_cost <= c2) {
          continue;
        }
        if (memo[x+dx[i]][y+dy[i]] == -1 || memo[x+dx[i]][y+dy[i]] > c2) {
          que.push(mp(mp(x+dx[i],y+dy[i]),c2));
        }
      }
    }
  }
  return now_cost;
}

int main()
{
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cin >> W >> H;
  rep(i,H){
    cin >> board[i];
  }
  {
    int g = -1;
    rep(i,H){
      rep(j,W){
        if (group[i][j] == 0){
          dfs(i,j,g);
          g += 1;
        }
      }
    }
  }
  int ans = INF;
  rep(i1,H){
    rep(j1,W){
      if (group[i1][j1] == 0) {
        continue;
      }
      rep(i2,H){
        rep(j2,W){
          if (group[i2][j2] == 0) {
            continue;
          }
          if (group[i1][j1] != group[i2][j2]) {
            ans = min(ans, search(i1,j1,i2,j2));
          }
        }
      }
    }
  }
  cout << ans << endl;
  return 0;
}