//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#define rep(i, n) for(int i=0; i<n; ++i)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
using namespace std;
using ll = int64_t;
using ld = long double;
using P = pair<int, int>;
using vs = vector<string>;
using vi = vector<int>;
using vvi = vector<vi>;
template<class T> using PQ = priority_queue<T>;
template<class T> using PQG = priority_queue<T, vector<T>, greater<T> >;
const int INF = 100010001;
const ll LINF = (ll)INF*INF*10;
template<typename T1, typename T2>
inline bool chmax(T1 &a, T2 b) {return a < b && (a = b, true);}
template<typename T1, typename T2>
inline bool chmin(T1 &a, T2 b) {return a > b && (a = b, true);}
template<typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) { return is >> p.first >> p.second;}
template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) { return os << p.first << ' ' << p.second;}

const int N = 3010;

//head

int h, w;
string s[N];
int di[] = {1, 0, -1, 1, -1, 1, 0, -1};
int dj[] = {-1, -1, -1, 0, 0, 1, 1, 1};
inline bool able(int i, int j) {return i >= 0 and j >= 0 and i < h and j < w;}
queue<P> q;
int dist[N][N];
int ans;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cin >> h >> w;
	rep(i, h) cin >> s[i+1];
	rep(i, h) s[i+1] = "." + s[i+1] + ".";
	s[0] = s[h+1] = string(w+2, '.');
	h += 2;
	w += 2;

	//rep(i, h) cout << s[i] << endl;

	rep(i, h) fill(dist[i], dist[i]+w, INF);
	rep(i, h) rep(j, w) {
		if(s[i][j] == '.') {
			dist[i][j] = 0;
			q.emplace(i, j);
		}
	}

	while(!q.empty()) {
		P now = q.front();
		q.pop();
		int ni = now.first, nj = now.second;

		rep(i, 8) {
			int mi = ni+di[i];
			int mj = nj+dj[i];
			if(able(mi, mj) and dist[mi][mj] == INF) {
				dist[mi][mj] = dist[ni][nj]+1;
				q.emplace(mi, mj);
			} 
		}
	}

	rep(i, h) rep(j, w) chmax(ans, dist[i][j]);

	cout << ans << endl;
}