#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include "bits/stdc++.h"
#define REP(i,a,b) for(i=a;i<b;++i)
#define rep(i,n) REP(i,0,n)
#define ll long long
#define ull unsigned ll
typedef long double ld;
#define ALL(a) (a).begin(),(a).end()
#define ifnot(a) if(not a)
#define dump(x)  cerr << #x << " = " << (x) << endl
using namespace std;

void reader(int &a) { scanf("%d", &a); }
void reader(double &a) { scanf("%lf", &a); }
void reader(char a[]) { scanf("%s", a); }
void reader(char &a) { scanf(" %c", &a); }
void reader(ll &a) { scanf("%lld", &a); }
void reader(ull &a) { scanf("%llu", &a); }
// void reader(string& a){cin >> a;};
template<class T, class U> void reader(T& t, U& u) { reader(t); reader(u); }
template<class T, class U, class V> void reader(T& t, U& u, V& v) { reader(t); reader(u); reader(v); }

void writer(const int a, char c) { printf("%d", a); putchar(c); }
void writer(const ll a, char c) { printf("%lld", a); putchar(c); }
void writer(const ull a, char c) { printf("%llu", a); putchar(c); }
void writer(const double a, char c) { printf("%.20lf", a); putchar(c); }
void writer(const char a[]) { printf("%s", a); };
void writer(const char a[], char c) { printf("%s", a); putchar(c); };
void writer(const char a, char c) { putchar(a); putchar(c); };
template<class T> void writerLn(T t) { writer(t, '\n'); }
template<class T, class U> void writerLn(T t, U u) { writer(t, ' '); writer(u, '\n'); }
template<class T, class U, class V> void writerLn(T t, U u, V v) { writer(t, ' '); writer(u, ' '); writer(v, '\n'); }
template<class T> void writerArr(T x[], int n) { int i; if (!n) { putchar('\n'); return; }rep(i, n - 1) writer(x[i], ' '); writer(x[n - 1], '\n'); }
template<class T> void writerVec(vector<T> x) { int n = x.size(); int i; if (!n) { putchar('\n'); return; }rep(i, n - 1) writer(x[i], ' '); writer(x[n - 1], '\n'); }

vector<string> split(const string &str, char sep) { vector<string> v; stringstream ss(str); string buffer; while (getline(ss, buffer, sep)) { v.push_back(buffer); }return v; }
// #define int ll
bool test = 0;
int dx[] = { 0,1,0,-1 };
int dy[] = { 1,0,-1,0 };
#define INF (1 << 28)
ull mod = (int)1e9 + 7;
//.....................
#define MAX (int)1e6 + 5

char field[3005][3005];
int fieldv[3005][3005];

int H, W;

struct Point {
	int y, x, cnt;
};

void grid_bfs() {
	int i, j;
	Point s;
	//.............
	queue<Point> q;
	cin >> H >> W;
	REP(i, 1, H + 1) {
		char buf[3005];
		reader(buf);
		field[i][0] = ' ';
		strcpy(field[i] + 1, buf);
	}
	rep(i, H + 1) rep(j, W + 1) fieldv[i][j] = INF;
	REP(i, 1, H+1) REP(j, 1, W+1) {
		char c = field[i][j];
		if (c == '.') {
			q.push({ i,j,0 });
			fieldv[i][j] = 0;
		}
	}
	rep(i, H+2) {
		fieldv[i][0] = 0;
		q.push({ i,0,0 });
	}
	rep(i, H+2) {
		fieldv[i][W + 1] = 0;
		q.push({ i,W + 1,0 });
	}
	rep(i, W+2) {
		fieldv[0][i] = 0;
		q.push({ 0,i,0 });
	}
	rep(i, W+2) {
		fieldv[H + 1][i] = 0;
		q.push({ H + 1,i,0 });
	}
	//..............
	while (q.size()) {
		auto now = q.front(); q.pop();
		Point next = now;
		next.cnt++;
		REP(i,-1,2) REP(j,-1,2) {
			next.x = now.x + i;
			next.y = now.y + j;
			if (next.x < 0 || W + 1 <= next.x) continue;
			if (next.y < 0 || H + 1 <= next.y) continue;
			if (fieldv[next.y][next.x] > next.cnt) {
				fieldv[next.y][next.x] = next.cnt;
				q.push(next);
			}
		}
	}
}
signed main(void)
{
	int i, j, k, l;
	grid_bfs();
	int a = 0;
	rep(i, H + 1) rep(j, W + 1) {
		if (fieldv[i][j] > a) a = fieldv[i][j];
	}
	cout << a << endl;
	//rep(i, H + 2) {
	//	rep(j, W + 2) {
	//		cout << fieldv[i][j] << " ";
	//	}
	//	cout << endl;
	//}
	return 0;
}