#include <iostream>
#include <string>
#include <vector>
using namespace std;

bool tof,tof2;
int h, w;

int solve(int cnt, vector<vector<int> > &land) {
	tof2 = false;
	for (int i = 0; i < h+2; i++) {
		for (int j = 0; j < w + 2; j++) {
			if (land[i][j] == cnt) {
				for (int a = -1; a < 2; a++) {
					for (int b = -1; b < 2; b++) {
						if (i + a > h + 1 || j + b > w + 1 || i + a < 0 || j + b < 0) continue;
						if (land[i + a][j + b] == 1) {
							tof2 = true;
							land[i + a][j + b] = cnt + 2;
						}
					}
				}
			}
		}
	}
	if (!tof2) return cnt;

	cnt = solve(cnt+2, land);

	return cnt;
}

int main()
{
	cin >> h >> w;
	vector<vector<int> > land;
	land.resize(h + 2);
	for (int i = 0; i < h + 2; i++) {
		land[i].resize(w+2);
	}

	for (int i = 1; i < h + 1; i++) {
		string s;
		cin >> s;
		for (int j = 0; j < w; j++) {
			if (s[j] == '#') land[i][j+1] = 1;
		}
	}
	int cnt = 0;

	cout << solve(cnt, land)/2 << endl;

    return 0;
}