#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream> 
#include<map>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <iomanip>
using namespace std;
#define MAX_MOD 1000000007
#define REP(i,n) for(int i = 0;i < n;++i)
long long dijk[5000][5000] = {};
bool ok[5000][5000] = {};
int main() {
	int h, w;
	cin >> h >> w;
	queue<pair<int, int>> go[2];
	for (int i = 1;i <= h;++i) {
		go[0].push(make_pair(i,0));
		go[0].push(make_pair(i, w + 1));
	}
	for (int i = 1;i <= w;++i) {
		go[0].push(make_pair(0, i));
		go[0].push(make_pair(h + 1, i));
	}
	REP(i, h) {
		string hoge;
		cin >> hoge;
		REP(q, w) {
			if (hoge[q] == '.') {
				ok[i + 1][q + 1] = 1;
				go[0].push(make_pair(i + 1, q + 1));
			}
			else {
				dijk[i + 1][q + 1] = -1;
			}
		}
	}
	for (int i = 0;i >= 0;++i) {
		if (go[i % 2].empty() == true) {
			cout << i-1 << endl;
			return 0;
		}
		while (go[i % 2].empty() == false) {
			pair<int, int> now = go[i % 2].front();
			go[i % 2].pop();
			if (dijk[now.first+1][now.second] == -1) {
				go[(i + 1) % 2].push(make_pair(now.first + 1, now.second));
				dijk[now.first + 1][now.second] = i+1;
			}
			if (now.first != 0&&dijk[now.first - 1][now.second] == -1) {
				go[(i + 1) % 2].push(make_pair(now.first - 1, now.second));
				dijk[now.first - 1][now.second] = i+1;
			}
			if (dijk[now.first][now.second + 1] == -1) {
				go[(i + 1) % 2].push(make_pair(now.first, now.second + 1));
				dijk[now.first][now.second + 1] = i+1;
			}
			if (now.second != 0&&dijk[now.first][now.second - 1] == -1) {
				go[(i + 1) % 2].push(make_pair(now.first, now.second - 1));
				dijk[now.first][now.second - 1] = i+1;
			}
			if (dijk[now.first + 1][now.second + 1] == -1) {
				go[(i + 1) % 2].push(make_pair(now.first + 1, now.second + 1));
				dijk[now.first + 1][now.second + 1] = i + 1;
			}
			if (now.first != 0&&dijk[now.first - 1][now.second + 1] == -1) {
				go[(i + 1) % 2].push(make_pair(now.first - 1, now.second + 1));
				dijk[now.first - 1][now.second + 1] = i + 1;
			}
			if (now.second != 0 && dijk[now.first + 1][now.second - 1] == -1) {
				go[(i + 1) % 2].push(make_pair(now.first + 1, now.second - 1));
				dijk[now.first + 1][now.second - 1] = i + 1;
			}
			if (now.second != 0 && now.first != 0 && dijk[now.first - 1][now.second - 1] == -1) {
				go[(i + 1) % 2].push(make_pair(now.first - 1, now.second - 1));
				dijk[now.first - 1][now.second - 1] = i + 1;
			}
		}
	}
}