#ifdef LOCAL111
#else
	#define NDEBUG
#endif
#include <bits/stdc++.h>
const int INF = 1e8;
using namespace std;

#define endl '\n'
#define ALL(a)  (a).begin(),(a).end()
#define SZ(a) int((a).size())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n)  FOR(i,0,n)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define RBP(i,a) for(auto& i : a)
#ifdef LOCAL111
	#define DEBUG(x) cout<<#x<<": "<<(x)<<endl
#else
	#define DEBUG(x) true
#endif
#define F first
#define S second
#define SNP string::npos
#define WRC(hoge) cout << "Case #" << (hoge)+1 << ": "
#define rangej(a,b,c) ((a) <= (c) and (c) < (b))
#define rrangej(b,c) rangej(0,b,c)
template<typename T> void pite(T a, T b){ for(T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite; cout << endl;}
template<typename T> bool chmax(T& a, T b){if(a < b){a = b; return true;} return false;}
template<typename T> bool chmin(T& a, T b){if(a > b){a = b; return true;} return false;}

typedef pair<int,int> P;
typedef long long int LL;
typedef unsigned long long ULL;
typedef pair<LL,LL> LP;

void ios_init(){
	//cout.setf(ios::fixed);
	//cout.precision(12);
#ifdef LOCAL111
	return;
#endif
	ios::sync_with_stdio(false); cin.tie(0);	
}

int h,w;

/*int dist_s(vecotr<vecor<int>>& dp, int px, int py)
{
	FOR(dx,-1,2) FOR(dy,-1,2){
		if(dx == 0 and dy == 0) continue;

	}
}*/

bool check(int x, int y){
	return 0 <= x and x < h and 0 <= y and y < w;
}

int main()
{
	ios_init();
	cin >> h >> w;
	vector<string> s(h+2);
	s[0] = string(w+2, '.');
	FOR(i,1,h+1) cin >> s[i], s[i] = "."+s[i]+".";
	s[h+1] = string(w+2, '.');
	DEBUG(0);
	h += 2; w += 2;
	vector<vector<int>> dp(h, vector<int>(w, INF));
	using T = tuple<int, int, int>;
	queue<T> qu;
	DEBUG(1);
	REP(i,h) REP(j,w) if(s[i][j] == '.') qu.emplace(i,j,0);
	DEBUG(2);
	while(!qu.empty()){
		P curr;
		int dist;
		tie(curr.F, curr.S, dist) = qu.front();
		qu.pop();
		if(dp[curr.F][curr.S] != INF) continue;
		dp[curr.F][curr.S] = dist;
		FOR(dx,-1,2) FOR(dy,-1,2){
			int nx = curr.F+dx, ny = curr.S+dy;
			if((dx == 0 and dy == 0) or !(check(nx, ny))) continue;
			if(dp[nx][ny] == INF) qu.emplace(nx, ny, dist+1);
		}
	}
	int ans = 0;
	REP(i,h) REP(j,w) ans = max(ans, dp[i][j]);
	cout << ans << endl; 
	return 0;
}