#include <cstdio>
#include <iostream>
#include <vector>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <string>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <functional>
#include <queue>
#include <stack>
#include <cmath>
#include <iomanip>
#include <list>
#include <tuple>
#include <bitset>
#include <ciso646>
#include <cassert>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> T;
typedef vector<ll> vec;

inline bool check(ll x, ll y, ll xMax, ll yMax) { return x >= 0 && y >= 0 && xMax > x && yMax > y; }
inline int toint(string s) { int v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string tostring(T x) { ostringstream sout; sout << x; return sout.str(); }
template<class T> inline T sqr(T x) { return x*x; }
template<class T> inline T mypow(T x, ll n) { T res = 1; while (n > 0) { if (n & 1)res = res * x;	x = x * x;	n >>= 1; }return res; }
inline ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }
inline ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }

#define For(i,a,b)	for(ll (i) = (a);i < (b);(i)++)
#define rep(i,n)	For(i,0,n)
#define rFor(i,a,b)	for(ll (i) = (a-1);i >= (b);(i)--)
#define rrep(i,n)	rFor(i,n,0)
#define each(i,n)	for(auto &i : n)
#define clr(a)		memset((a), 0 ,sizeof(a))
#define mclr(a)		memset((a), -1 ,sizeof(a))
#define all(a)		(a).begin(),(a).end()
#define sz(a)		(sizeof(a))
#define tostr(a)	tostring(a)
#define dump(val) 	cerr << #val " = " << val << endl;
#define Fill(a,v)	fill((int*)a,(int*)(a+(sz(a)/sz(*(a)))),v)

const ll dx[8] = { 1, 0, -1, 0, 1, 1, -1, -1 }, dy[8] = { 0, 1, 0, -1, -1, 1, -1, 1 };

const ll mod = 1e9 + 7;
const ll INF = 1e17 + 9;

#define int ll
#define double ld

void surround(vector<string> &vs, int &h, int &w, char c) {
	vector<string> vs2;
	vs2.push_back(string(w + 2, c));
	rep(i, h) {
		vs2.push_back(string());
		vs2[i + 1] = c + vs[i] + c;
	}
	vs2.push_back(string(w + 2, c));
	h += 2, w += 2;
	vs = vs2;
}

int d[3501][3501];

signed main() {
	int h, w;
	cin >> h >> w;
	vector<string> s(h);
	rep(y, h) {
		cin >> s[y];
	}
	surround(s, h, w, '.');
	Fill(d, INF);
	queue<P> q;
	rep(y, h)rep(x, w) {
		if (s[y][x] == '.') {
			d[y][x] = 0;
			q.push(P(y, x));
		}
	}
	int ans = 0;
	while (q.size()) {
		int y = q.front().first;
		int x = q.front().second;
		q.pop();
		rep(i, 8) {
			int ty = y + dy[i], tx = x + dx[i];
			if (check(tx, ty, w, h)) {
				if (d[ty][tx] > d[y][x] + 1) {
					d[ty][tx] = d[y][x] + 1;
					q.push(P(ty, tx));
					ans = max(ans, d[ty][tx]);
				}
			}
		}
	}

	cout << ans << endl;

	return 0;
}