#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;
	int mn, mx;
	for (int i = 1; i < h+1; i++) {
		for (int j = 1; j < w + 1; j++) {
			if (land[i][j] == cnt) {
				tof = false;
				for (int a = -1; a < 2; a++) {
					for (int b = -1; b < 2; b++) {
						if (land[i + a][j + b] < cnt) {
							tof = true;
							break;
						}
					}
					if (tof) break;
				}
				if (!tof) {
					land[i][j]++;
					tof2 = true;
				}
			}
		}
	}
	if (!tof2) return cnt;

	cnt = solve(++cnt, 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] = 0;
			else if (s[j] == '#') land[i][j+1] = 1;
		}
	}
	int cnt = 1;

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

    return 0;
}