#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
//#define int long long
using namespace std;

int H, W;
char grid[3000][3000];
set<pair<int, int> > riku;
int di[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int dj[8] = {-1, 0, 1, -1, 1, -1, 0, 1};

//海に隣接していたらtrueを返す
bool check(int i, int j)
{
	rep(ii,8)
	{
		int ni = i + di[ii];
		int nj = j + dj[ii];
		if (ni < 0 || H <= ni || nj < 0 || W <= nj)
		{
			return true;
		}
		if (grid[ni][nj] == '.')
		{
			return true;
		}
	}
	return false;
}

signed main()
{
	cin >> H >> W;
	rep(i,H)
	{
		cin >> grid[i];
	}

	rep(i,H)
	{
		rep(j,W)
		{
			if (grid[i][j] == '#')
			{
				riku.insert(pair<int, int>(i, j));
			}
		}
	}

	int ans = 0;
	while (!riku.empty())
	{
		//printf("riku.size() = %d\n", riku.size());
		ans++;
		set<pair<int, int> > new_riku;
		set<pair<int, int> > unimisuru;

		set<pair<int, int> >::iterator it = riku.begin();
		while (it != riku.end())
		{
			if (check(it->first, it->second))
			{
				unimisuru.insert(pair<int, int>(it->first, it->second));
				//grid[it->first][it->second] = '.';
			}
			else
			{
				new_riku.insert(pair<int, int>(it->first, it->second));
			}
			++it;
		}

		it = unimisuru.begin();
		while (it != unimisuru.end())
		{
			grid[it->first][it->second] = '.';
			++it;
		}

		riku = new_riku;
	}

	cout << ans << endl;
}