#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

int h, w;
string maps[3000];
int d[3000][3000];

struct Data {
	int d, y, x, sy, sx;
	bool operator > (const Data &r) const {
		if (d != r.d) return d > r.d;
		if (y != r.y) return y > r.y;
		if (x != r.x) return x > r.x;
		if (sy != r.sy) return sy > r.sy;
		return sx > r.sx;
	}
};

int main() {
	cin >> h >> w;
	REP(i, h) cin >> maps[i];
	
	fill(d[0], d[h], INF);
	
	priority_queue<Data, vector<Data>, greater<Data> > pq;
	
	REP(i, h) {
		pq.push( (Data){ 1, i, 0, i, -1 } );
		pq.push( (Data){ 1, i, w - 1, i, w } );
	}
	REP(j, w) {
		pq.push( (Data){ 1, 0, j, -1, j } );
		pq.push( (Data){ 1, h - 1, j, h, j } );
	}
	REP(i, h) REP(j, w) if (maps[i][j] == '.') pq.push( (Data){ 0, i, j, i, j } );
	
	while (!pq.empty()) {
		Data now = pq.top(); pq.pop();
		
		if (!chmin(d[now.y][now.x], now.d)) continue;
		
		int dx[4] = {1,0,-1,0}, dy[4] = {0,1,0,-1};
		REP(i, 4) {
			int nx = now.x + dx[i];
			int ny = now.y + dy[i];
			if (!(nx >= 0 && nx < w && ny >= 0 && ny < h)) continue;
			
			int nd = max(abs(nx - now.sx), abs(ny - now.sy));
			if (d[ny][nx] <= nd) continue;
			
			pq.push( (Data){ nd, ny, nx, now.sy, now.sx} );
		}
	}
	
	int ans = 0;
	REP(i, h) REP(j, w) chmax(ans, d[i][j]);
	cout << ans << endl;
	
	return 0;
}