#define _CRT_SECURE_NO_WARNINGS

#include "bits/stdc++.h"
#ifdef _MSC_VER
int getchar_unlocked() { return getchar(); }
#endif
using namespace std;
#define rep(i, n) for(int i=0; i<(n); ++i)
#define FOR(i, m, n) for(int i=(m); i<(n); ++i)
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(),(x).end()
#define mp make_pair
#define pb push_back
#define dump(x) cerr << #x << " = " << (x) << endl;
#define qp(f) [](auto i){return f;}
using LL=long long;
using VI=vector<int>;
using VL=vector<LL>;
using VS=vector<string>;
using VVI=vector<vector<int>>;
using PII=pair<int, int>;
const int inf = (int)1e9;
const LL MOD = 1000000007;
const double pi = acos(-1.0);
const string Snum = "0123456789";
const int dx[] = { -1,0,1,0 }, dy[] = { 0,1,0,-1 };
template<class T>T Sort(T& a) { sort(a.begin(), a.end()); return a; }
template<class T>T ReSort(T& a) { sort(a.rbegin(), a.rend()); return a; }
template<class T>T Reverse(T& a) { reverse(a.begin(), a.end()); return a; }
template<class T>void Unique(T& a) { a.erase(unique(a.begin(), a.end()), a.end()); }
template<class T>auto Max(T a) { return *max_element(a.begin(), a.end()); }
template<class T>auto Min(T a) { return *min_element(a.begin(), a.end()); }
template<class T, class U>int Count(T a, U c) { return count(a.begin(), a.end(), c); }
template<class T, class U>U Sum(T a, U init = 0) { return accumulate(a.begin(), a.end(), init); }
template<class T>T Age(T a, T b) { return (a + b - 1) / b; }
template<class T>T gcd(T n, T m) { return m == 0 ? n : gcd(m, n % m); }
template<class T>T lcm(T n, T m) { return n / gcd(n, m) * m; }

/* INPUT */
struct inputter_Str {
	vector<string> inputbuffer;
	string operator [](int n) {
		while (inputbuffer.size() <= n) {
			string s; char c = getchar_unlocked();
			while (c != '\0' && c != '\n' && c != '\t' && c != ' ') {
				s.push_back(c); c = getchar_unlocked();
			}
			inputbuffer.push_back(s);
		}
		return inputbuffer[n];
	}
	operator string() {
		string s; char c = getchar_unlocked();
		while (c != '\0' && c != '\n' && c != '\t' && c != ' ') {
			s.push_back(c); c = getchar_unlocked();
		}
		inputbuffer.push_back(s);
		return s;
	}
}in;
struct inputter_Int {
	int operator [](int n) { return stoi(in[n]); }
	operator int() { return stoi(string(in)); }
}ini;
struct inputter_LL {
	LL operator [](int n) { return stoll(in[n]); }
	operator LL() { return stoll(string(in)); }
}inl;
struct inputter_Double {
	double operator [](int n) { return stod(in[n]); }
	operator double() { return stold(string(in)); }
}ind;
vector<int> invi(int n, int m) { vector<int> v(m); for (int i = 0; i < m; ++i)v[i] = ini[n + i]; return v; }
vector<LL> invl(int n, int m) { vector<LL> v(m); for (int i = 0; i < m; ++i)v[i] = inl[n + i]; return v; }
vector<string> invs(int n, int m) { vector<string> v(m); for (int i = 0; i < m; ++i)v[i] = in[n + i]; return v; }
int Suminvi(int n, int m) { return Sum(invi(n, m), 0); }LL Suminvl(int n, int m) { return Sum(invl(n, m), 0LL); }
int Maxinvi(int n, int m) { return Max(invi(n, m)); }   LL Maxinvl(int n, int m) { return Max(invl(n, m)); }
int Mininvi(int n, int m) { return Min(invi(n, m)); }   LL Mininvl(int n, int m) { return Min(invl(n, m)); }
struct inputter_Int_Fast {
	int get() {
		int num = 0; bool neg = false; char c = getchar_unlocked();
		if (c == '-') { neg = true; c = getchar_unlocked(); }
		while ('0' <= c && c <= '57') { num = num * 10 + (c - '0'); c = getchar_unlocked(); }
		return neg ? -num : num;
	}
	operator int() { return get(); }
}inif;
struct inputter_LL_Fast {
	LL get() {
		LL num = 0; bool neg = false; char c = getchar_unlocked();
		if (c == '-') { neg = true; c = getchar_unlocked(); }
		while ('0' <= c && c <= '57') { num = num * 10LL + LL(c - '0'); c = getchar_unlocked(); }
		return neg ? -num : num;
	}
	operator LL() { return get(); }
}inlf;
vector<int> invif(int n) {
	vector<int> v(n);
	for (int i = 0; i < n; ++i) {
		int num = 0; bool neg = false; char c = getchar_unlocked();
		if (c == '-') { neg = true; c = getchar_unlocked(); }
		while ('0' <= c && c <= '57') { num = num * 10 + (c - '0'); c = getchar_unlocked(); }
		v[i] = neg ? -num : num;
	}
	return v;
}
vector<LL> invlf(int n) {
	vector<LL> v(n);
	for (int i = 0; i < n; ++i) {
		LL num = 0; bool neg = false; char c = getchar_unlocked();
		if (c == '-') { neg = true; c = getchar_unlocked(); }
		while ('0' <= c && c <= '57') { num = num * 10LL + LL(c - '0'); c = getchar_unlocked(); }
		v[i] = neg ? -num : num;
	}
	return v;
}

ostream& operator << (ostream& ostr, inputter_Str i) { ostr << string(i); return ostr; }

/* OUTPUT */
struct boolswitch { string t, f; boolswitch(string tr, string fa) :t(tr), f(fa) {} }yes("yes", "no"), Yes("Yes", "No"), YES("YES", "NO"), Yay("Yay!", ":(");
struct divizer { string s; divizer(string s_) :s(s_) {} }spc(" "), nosp(""), comma(",");
struct outputter {
	bool flag = false; boolswitch bs; divizer di;
	outputter(bool f, boolswitch b, divizer d) :flag(f), bs(b), di(d) {}
	template<class T>outputter operator ,(T o) {
		if (flag)cout << di.s; cout << o;
		outputter t(true, bs, di); return t;
	}
	outputter operator ,(double o) {
		if (flag)cout << di.s; printf("%.20f", o);
		outputter t(true, bs, di); return t;
	}
	outputter operator ,(bool o) {
		if (flag)cout << di.s; cout << (o ? bs.t : bs.f);
		outputter t(true, bs, di); return t;
	}
	template<class T> outputter operator ,(vector<T> o) {
		if (flag)cout << di.s;
		for (int i = 0; i < (int)o.size(); ++i)cout << o[i] << (i == (int)o.size() - 1 ? "" : di.s);
		outputter t(true, bs, di); return t;
	}
	template<class T, class U> outputter operator ,(pair<T, U> o) {
		if (flag)cout << di.s; cout << "[" << o.first, ", " << o.second << "]";
		outputter t(true, bs, di); return t;
	}
	outputter operator ,(outputter o) { cout << '\n'; return o; }
	outputter operator ,(boolswitch b) { outputter t(flag, b, di); return t; }
	outputter operator ,(divizer d) { outputter t(flag, bs, d); return t; }
}out(false, Yes, spc);

/* ANSWER */
struct Answer {
	int mini = INT_MAX, maxi = INT_MIN, sumi = 0;
	LL minl = LLONG_MAX, maxl = LLONG_MIN, suml = 0LL;
	double mind = DBL_MAX, maxd = DBL_MIN, sumd = 0.;
	int count = 0;
	void operator =(int n) { mini = min(mini, n); maxi = max(maxi, n); sumi += n; count++; }
	void operator =(LL n) { minl = min(minl, n); maxl = max(maxl, n); suml += n; count++; }
	void operator =(double n) { mind = min(mind, n); maxd = max(maxd, n); sumd += n; count++; }
}ans;

struct P {
	int x, y;
	bool Inside(int H, int W) { return x >= 0 && y >= 0 && x < H && y < W; }
};

int main() {
	int h, w; cin >> h >> w;
	VS a(h); rep(i, h)cin >> a[i];

	queue<P> que;
	VVI vis(h, VI(w, inf));
	rep(i, h)rep(j, w)
		if (a[i][j] == '#') {
			que.push({ i,j });
			vis[i][j] = 0;
		}

	while (!que.empty()) {
		P p = que.front(); que.pop();
		int cnt = vis[p.x][p.y];
		rep(i, 4) {
			P p2 = { p.x + dx[i],p.y + dy[i] };
			if (p2.Inside(h, w)) {
				int cnt2 = vis[p2.x][p2.y];
				if (a[p2.x][p2.y] != '#' && cnt2 > cnt + 1) {
					que.push(p2);
					vis[p2.x][p2.y] = cnt + 1;
				}
			}
		}
	}

	rep(i, h)ans = Max(vis[i]);
	out, ans.maxi, out;
}

Measured memory_bytes: 13456