# include "bits/stdc++.h"
using namespace std;
using LL = long long;
using ULL = unsigned long long;
const double PI = acos(-1);
template<class T>constexpr T INF() { return ::std::numeric_limits<T>::max(); }
template<class T>constexpr T HINF() { return INF<T>() / 2; }
template <typename T_char>T_char TL(T_char cX) { return tolower(cX); };
template <typename T_char>T_char TU(T_char cX) { return toupper(cX); };
const int vy[] = { -1, -1, -1, 0, 1, 1, 1, 0 }, vx[] = { -1, 0, 1, 1, 1, 0, -1, -1 };
const int dx[4] = { -1,0,1,0 }, dy[4] = { 0,-1,0,1 };
int popcnt(unsigned long long n) { int cnt = 0; for (int i = 0; i < 64; i++)if ((n >> i) & 1)cnt++; return cnt; }
int d_sum(LL n) { int ret = 0; while (n > 0) { ret += n % 10; n /= 10; }return ret; }
int d_cnt(LL n) { int ret = 0; while (n > 0) { ret++; n /= 10; }return ret; }
LL gcd(LL a, LL b) { if (b == 0)return a; return gcd(b, a%b); };
LL lcm(LL a, LL b) { LL g = gcd(a, b); return a / g*b; };
# define ALL(qpqpq)           (qpqpq).begin(),(qpqpq).end()
# define UNIQUE(wpwpw)        (wpwpw).erase(unique(ALL((wpwpw))),(wpwpw).end())
# define LOWER(epepe)         transform(ALL((epepe)),(epepe).begin(),TL<char>)
# define UPPER(rprpr)         transform(ALL((rprpr)),(rprpr).begin(),TU<char>)
# define FOR(i,tptpt,ypypy)   for(LL i=(tptpt);i<(ypypy);i++)
# define REP(i,upupu)         FOR(i,0,upupu)
# define INIT                 std::ios::sync_with_stdio(false);std::cin.tie(0)
# pragma warning(disable:4996)

int h, w;
char c[22][22];
char cc[22][22];
queue<pair<int, int>>q;
bool flg;
int d[22][22];

void dfs(int i, int j) {
	cc[i][j] = '#';
	d[i][j] = 0;
	q.push(make_pair(i, j));
	REP(k, 4) {
		int ni = i + dy[k];
		int nj = j + dx[k];
		if (cc[ni][nj] == '.')dfs(ni, nj);
	}
}

int main() {
	cin >> w >> h;
	LL ans = INF<int>();
	REP(i, h)REP(j, w) {
		cin >> c[i][j];
		cc[i][j] = c[i][j];
		d[i][j] = -1;
	}
	REP(i, h)REP(j, w) {
		if (c[i][j] == '.'&&!flg) {
			dfs(i, j);
			flg = true;
		}
	}
	while (!q.empty()) {
		auto p = q.front();
		//cout << p.first << " " << p.second << endl;
		q.pop();
		REP(k, 4) {
			int ni = p.first + dy[k];
			int nj = p.second + dx[k];
			if (d[ni][nj] == -1) {
				d[ni][nj] = d[p.first][p.second] + 1;
				if (c[ni][nj] == '.') {
					cout << d[ni][nj]-1 << endl;
					//system("pause");
					return 0;
				}
				q.push(make_pair(ni, nj));
			}
		}
	}
	//system("pause");
}