#include <bits/stdc++.h>
using namespace std;

#define int long long

const int INF = LLONG_MAX/2;
const int dx[] = {1, 1, 1, 0, -1, -1, -1, 0}, dy[] = {-1, 0, 1, 1, 1, 0, -1, -1};

int H, W;
char fld[3002][3002];
bool isUsed[3002][3002];

signed main()
{
	fill(fld[0], fld[0] + 3002*3002, '.');
	cin >> H >> W;
	queue< pair< pair<int, int>, int> > q;
	for (int i = 1; i < H + 1; i++)
	{
		for (int j = 1; j < W + 1; j++)
		{
			cin >> fld[i][j];
		}
	}
	for (int i = 0; i < H + 2; i++)
	{
		for (int j = 0; j < W + 2; j++)
		{
			if (fld[i][j] == '.') q.emplace(make_pair(make_pair(j, i), 0));
		}
	}
	int ma = 0;
	while (!q.empty())
	{
		pair<int, int> p = q.front().first;
		int cost = q.front().second;
		q.pop();
		isUsed[p.second][p.first] = true;
		ma = cost;
		for (int i = 0; i < 8; i++)
		{
			int nx = p.first + dx[i], ny = p.second + dy[i];
			if (nx < 0 || W + 2 <= nx || ny < 0 || H + 2 <= ny || isUsed[ny][nx]) continue;
			isUsed[ny][nx] = true;
			q.emplace(make_pair(make_pair(nx, ny), cost + 1));
		}
	}
	printf("%lld\n", ma);
	return 0;
}