//サンプルがやさしい(な阪関)
#include <iostream>
#include <algorithm>
#include <tuple>
#include <queue>
#include <cstdio>
using namespace std;

int h, w;
char s[3002][3002];

int dy[8] = {-1, -1, -1,  0,  0,  1,  1,  1};
int dx[8] = {-1,  0,  1, -1,  1, -1,  0,  1};
int cost[3002][3002];

void input() {
	//番兵する
	cin >> h >> w;
	h += 2;
	w += 2;
	
	for (int i = 0; i < h; i++) { 
		for (int j = 0; j < w; j++) {
			s[i][j] = '.';
		}
	}
	
	for (int i = 1; i < h - 1; i++) { scanf("%s", s[i] + 1); s[i][w-1] = '.'; }
	
	for (int i = 0; i < h; i++) {
		for (int j = 0; j < w; j++) {
			cost[i][j] = 1145141919;
		}
	}
}

bool is_range(int y, int x) {
	return (0 <= y && y < h && 0 <= x && x < w);
}

void bfs() {
	typedef tuple<int, int, int> T;	//cost, y, x
	static queue<T> que;
	
	//全ての海を始点にする
	for (int i = 0; i < h; i++) {
		for (int j = 0; j < w; j++) {
			if (s[i][j] == '.') {
				que.push(T(0, i, j));
				cost[i][j] = 0;
			}
		}
	}

	while (!que.empty()) {
		T now = que.front();
		que.pop();
		
		int cst = get<0>(now);
		int y = get<1>(now);
		int x = get<2>(now);
		
		for (int dir = 0; dir < 8; dir++) {
			int ny = y + dy[dir];
			int nx = x + dx[dir];
			if (is_range(ny, nx) && cost[ny][nx] > cst + 1) {
				que.push(T(cst + 1, ny, nx));
				cost[ny][nx] = cst + 1;
			}
		}
	}
}

int answer() {
	int ans = -1;
	for (int i = 0; i < h; i++) {
		for (int j = 0; j < w; j++) {
			ans = max(ans, cost[i][j]);
		}
	}
	return ans;
}

int main() {
	input();
	bfs();
	cout << answer() << endl;
	return 0;
}