#include <iostream>
#include <iomanip>
#include <sstream>
#include <vector>
#include <string>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <stack>
#include <queue>
#include <deque>
#include <algorithm>
#include <functional>
#include <iterator>
#include <limits>
#include <numeric>
#include <utility>
#include <cmath>
#include <cassert>
#include <cstdio>

using namespace std;
using namespace placeholders;

using LL = long long;
using ULL = unsigned long long;
using VI = vector< int >;
using VVI = vector< vector< int > >;
using VS = vector< string >;
using SS = stringstream;
using PII = pair< int, int >;
using VPII = vector< pair< int, int > >;
template < typename T = int > using VT = vector< T >;
template < typename T = int > using VVT = vector< vector< T > >;
template < typename T = int > using LIM = numeric_limits< T >;

template < typename T > inline istream& operator>>( istream &s, vector< T > &v ){ for ( T &t : v ) { s >> t; } return s; }
template < typename T > inline ostream& operator<<( ostream &s, const vector< T > &v ){ for ( int i = 0; i < int( v.size() ); ++i ){ s << ( " " + !i ) << v[i]; } return s; }
template < typename T > inline T fromString( const string &s ) { T res; istringstream iss( s ); iss >> res; return res; }
template < typename T > inline string toString( const T &a ) { ostringstream oss; oss << a; return oss.str(); }

#define REP2( i, n ) REP3( i, 0, n )
#define REP3( i, m, n ) for ( int i = ( int )( m ); i < ( int )( n ); ++i )
#define GET_REP( a, b, c, F, ... ) F
#define REP( ... ) GET_REP( __VA_ARGS__, REP3, REP2 )( __VA_ARGS__ )
#define FOR( e, c ) for ( auto &&e : c )
#define ALL( c ) begin( c ), end( c )
#define AALL( a, t ) ( t* )a, ( t* )a + sizeof( a ) / sizeof( t )
#define DRANGE( c, p ) ( c ).begin(), ( c ).begin() + ( p ), ( c ).end()

#define SZ( v ) ( (int)( v ).size() )
#define EXIST( c, e ) ( ( c ).find( e ) != ( c ).end() )

template < typename T > inline bool chmin( T &a, const T &b ){ if ( b < a ) { a = b; return true; } return false; }
template < typename T > inline bool chmax( T &a, const T &b ){ if ( a < b ) { a = b; return true; } return false; }

#define PB push_back
#define EM emplace
#define EB emplace_back
#define BI back_inserter

#define MP make_pair
#define fst first
#define snd second

#define DUMP( x ) cerr << #x << " = " << ( x ) << endl

constexpr int INF = LIM<>::max() / 2;

int main()
{
	cin.tie( 0 );
	ios::sync_with_stdio( false );
	cout << setprecision( 12 ) << fixed;

	int H, W;
	cin >> H >> W;

	VS board( H );
	cin >> board;

	const auto inside = [=]( const int y, const int x ){ return 0 <= y && y < H && 0 <= x && x < W; };

	VVI distances( H, VI( W, INF ) );

	queue< PII > que;
	REP( i, H )
	{
		que.EM( i, -1 );
		que.EM( i, W );
	}
	REP( j, W )
	{
		que.EM( -1, j );
		que.EM( H, j );
	}
	REP( i, H )
	{
		REP( j, W )
		{
			if ( board[i][j] == '.' )
			{
				distances[i][j] = 0;
				que.EM( i, j );
			}
		}
	}

	while ( !que.empty() )
	{
		const int y = que.front().fst;
		const int x = que.front().snd;
		que.pop();

		const int d = inside( y, x ) ? distances[y][x] : 0;
		
		REP( dy, -1, 2 )
		{
			REP( dx, -1, 2 )
			{
				if ( !( dy | dx ) )
				{
					continue;
				}

				const int ny = y + dy;
				const int nx = x + dx;

				if ( inside( ny, nx ) && d+ 1 < distances[ ny ][ nx ] )
				{
					distances[ ny ][ nx ] = d + 1;
					que.EM( ny, nx );
				}
			}
		}
	}

	int res = 0;
	for_each( ALL( distances ), [&]( const VI &row ){ chmax( res, *max_element( ALL( row ) ) ); } );
	cout << res << endl;

	return 0;
}