#include <iostream>
#include <cstdio>
#include <vector>
#include <cmath>
#include <cstring>
#include <numeric>
#include <algorithm>
#include <functional>
#include <array>
#include <map>
#include <queue>
using namespace std;

#define Getsign(n) ((n > 0) - (n < 0))

typedef vector<int> Ivec;
typedef pair<int, int> Pos;

const pair<int, int> dir[8] = { {0,1},{1,1}, {1,0},{0,-1},{-1,-1},{1,-1},{-1,1}, {-1,0} };

#define MAX(a,b) (((a)>(b))?(a):(b))

#define Chebi(a,b) (MAX(abs(a.first-b.first),abs(a.second-b.second))) 
int main() {
	int h, w;
	scanf("%d %d%*c", &h, &w);
	int map[3004][30004] = {};
	Pos poss[3004][3004];
	queue<Pos> wf;
	for (int i = 2; h + 1 >= i; i++) {
		for (int j = 2; w + 1 >= j; j++) {
			char c;
			scanf("%c", &c);
			map[i][j] = c == '#' ? 1 : 0;
			if (c == '.') {
				wf.push({ i,j });
				poss[i][j] = { i,j };
			}
		}
		scanf("%*c");
	}
	for (int i = 1; h + 2 >= i; i++) {
		wf.push({ 1, i });
		wf.push({ h + 2, i });
		poss[1][i] = { 1, i };
		poss[h + 2][i] = {h+2, i};
	}
	for (int i = 1; w + 2 >= i; i++) {
		wf.push({ i, 1 });
		wf.push({i,w+2 });
		poss[i][1] = { i,1};
		poss[i][w+2] = {i, w + 2};
	}
	while (!wf.empty()) {
		Pos sea = wf.front();
		wf.pop();
		for (int i = 0; 8 > i; i++) {
			Pos tar = { sea.first + dir[i].first ,sea.second + dir[i].second };
			if (map[tar.first][tar.second] == 1) {
				if (poss[tar.first][tar.second].first == 0 || (Chebi(tar, poss[sea.first][sea.second]) < Chebi(tar, poss[tar.first][tar.second]))) {
					if (poss[tar.first][tar.second].first == 0 || poss[tar.first][tar.second].first != poss[sea.first][sea.second].first || poss[tar.first][tar.second].second != poss[sea.first][sea.second].second)
					{
						poss[tar.first][tar.second] = poss[sea.first][sea.second];
						wf.push(tar);
					}
				}
			}
		}
	}
	int maxim = -1;
	for (int i = 2; h + 1 >= i; i++) {
		for (int j = 2; w + 1 >= j; j++) {
			if (map[i][j] != 1)continue;
			Pos tar = { i,j };
			maxim = max(maxim, Chebi(poss[i][j], tar));
		}
	}
	printf("%d", maxim);
	return 0;
}