#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()
#define fi first
#define se second

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];

int main() {
	cin >> h >> w;
	REP(i, h) cin >> maps[i];
	
	fill(d[0], d[h], INF);
	
	priority_queue<P, vector<P>, greater<P> > pq;
	
	REP(i, h) {
		pq.push( P(1, pii(i, 0)) );
		pq.push( P(1, pii(i, w - 1)) );
		
		chmin(d[i][0], 1);
		chmin(d[i][w - 1], 1);
	}
	REP(j, w) {
		pq.push( P(1, pii(0, j)) );
		pq.push( P(1, pii(h - 1, j)) );
		
		chmin(d[0][j], 1);
		chmin(d[h - 1][j], 1);
	}
	REP(i, h) REP(j, w) if (maps[i][j] == '.') {
		pq.push( P(0, pii(i, j)) );
		chmin(d[i][j], 0);
	}
	
	while (!pq.empty()) {
		P now = pq.top(); pq.pop();
		
		int nd = now.fi;
		int x = now.se.se;
		int y = now.se.fi;
		
		FOR(dy, -1, 2) FOR(dx, -1, 2) {
			int nx = x + dx;
			int ny = y + dy;
			if (!(nx >= 0 && nx < w && ny >= 0 && ny < h)) continue;
			
			if (!chmin(d[ny][nx], nd + 1)) continue;
			pq.push( P(nd + 1, pii(ny, nx)) );
		}
	}
	
	int ans = 0;
	REP(i, h) REP(j, w) chmax(ans, d[i][j]);
	cout << ans << endl;
	
	return 0;
}