#include "bits/stdc++.h"
using namespace std;

bool check[30][30];
int dist[30][30];
int dy[] = {1, 0, -1, 0};
int dx[] = { 0, 1, 0, -1 };

int W, H;

bool ok(int y, int x){
	return y >= 0 && x >= 0 && y < H && x < W;
}

int main() {
	cin >> W >> H;
	vector<string> board(H);
	for (int i = 0; i < H; i++)
	{
		cin >> board[i];
	}

	queue<pair<int, int>> q;
	for (int i = 0; i < H; i++)
	{
		for (int j = 0; j < W; j++)
		{
			if (board[i][j] == '.'){
				check[i][j] = true;
				q.push(make_pair(i, j));
				break;
			}
		}
		if (!q.empty()) break;
	}

	while (!q.empty()){
		int y = q.front().first;
		int x = q.front().second;
		q.pop();
		for (int k = 0; k < 4; k++)
		{
			int ny = y + dy[k];
			int nx = x + dx[k];
			if (!ok(ny, nx)) continue;
			if (check[ny][nx]) continue;
			if (board[ny][nx] != '.') continue;
			check[ny][nx] = true;
			q.push(make_pair(ny, nx));
		}
	}

	for (int i = 0; i < H; i++)
	{
		for (int j = 0; j < W; j++)
		{
			if (board[i][j] == '.' && !check[i][j]){
				check[i][j] = true;
				q.push(make_pair(i, j));
				dist[i][j] = 0;
			}
			else dist[i][j] = 999;
		}
	}

	while (!q.empty()){
		int y = q.front().first;
		int x = q.front().second;
		q.pop();
		for (int k = 0; k < 4; k++)
		{
			int ny = y + dy[k];
			int nx = x + dx[k];
			if (!ok(ny, nx)) continue;
			if (dist[ny][nx] < 999) continue;

			if (board[ny][nx] == '.'){
				cout << dist[y][x] << endl;
				return 0;
			}
			check[ny][nx];
			q.push(make_pair(ny, nx));
			dist[ny][nx] = dist[y][x] + 1;
		}
	}

	cout << "error" << endl;
}