// Slower C++ solution:
#include <iostream>

#include <queue>

#include <cstring>

const int maxn=1010;

using namespace std;

struct Node {

	int x,y;

};

queue <Node> Q;

int a[maxn][maxn],d[maxn][maxn];

int vis[maxn][maxn];

int main(){

	memset(vis,0,sizeof(vis));

	memset(d,0,sizeof(d));

	ios::sync_with_stdio(false);

	cin.tie(0);

	int h,w;

	cin >> h>>w;

	for(int i=1;i<=h;i++){

		string s;

		cin >> s;

		for (int j=0;j<w;j++) {

			if (s[j] == '#'){

				a[i][j+1] = 1;

				Q.push((Node){i,j+1});

				vis[i][j+1] = 1;

			}else a[i][j+1] = 0;

			// a[i][j+1] = s[j]=='h'?1:0;



		}

	}



	int cnt = 0;

	while (!Q.empty()){

		Node p=Q.front();

		Q.pop();

		if (p.x>1 && !vis[p.x-1][p.y]){

			d[p.x-1][p.y] = d[p.x][p.y] + 1;

			Q.push((Node){p.x-1,p.y});

			vis[p.x-1][p.y] = 1;

		}

		if (p.y>1 && !vis[p.x][p.y-1]){

			d[p.x][p.y-1] = d[p.x][p.y] + 1;

			Q.push((Node){p.x,p.y-1});

			vis[p.x][p.y-1] = 1;

		}

		if (p.x<h && !vis[p.x+1][p.y]){

			d[p.x+1][p.y] = d[p.x][p.y] + 1;

			Q.push((Node){p.x+1,p.y});

			vis[p.x+1][p.y] = 1;

		}

		if (p.y<w && !vis[p.x][p.y+1]){

			d[p.x][p.y+1] = d[p.x][p.y] + 1;

			Q.push((Node){p.x,p.y+1});

			vis[p.x][p.y+1] = 1;

		}

	}

	int ans=0;

	// for (int i=1;i<=h;i++){

	// 	for (int j=1;j<=w;j++) ans=max(ans,d[i][j]),cout << d[i][j]<<' ';

	// 	cout << endl;

	// }

	for (int i=1;i<=h;i++)

		for (int j=1;j<=w;j++) ans=max(ans,d[i][j]);

	

	cout << ans;

}

// Faster C++ solution for the same problem (measured speedup: 1.8688942746115529x):
#include <bits/stdc++.h>

using namespace std;

void debug_out() { cerr << endl; }

template<class T> ostream& prnt(ostream& out, T v) { out << v.size() << '\n'; for(auto e : v) out << e << ' '; return out;}

template<class T> ostream& operator<<(ostream& out, vector <T> v) { return prnt(out, v); }

template<class T> ostream& operator<<(ostream& out, set <T> v) { return prnt(out, v); }

template<class T1, class T2> ostream& operator<<(ostream& out, map <T1, T2> v) { return prnt(out, v); }

template<class T1, class T2> ostream& operator<<(ostream& out, pair<T1, T2> p) { return out << '(' << p.st << ' ' << p.nd << ')'; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) { cerr << " " << H; debug_out(T...);}

#define dbg(...) cerr << #__VA_ARGS__ << " ->", debug_out(__VA_ARGS__)

#define dbg_v(x, n) do{cerr<<#x"[]: ";for(int _=0;_<n;++_)cerr<<x[_]<<" ";cerr<<'\n';}while(0)

#define dbg_ok cerr<<"OK!\n"

#define ll long long

#define ld long double

#define ull unsigned long long

#define pii pair<int,int>

#define MOD 1000000007

#define zeros(x) x&(x-1)^x

#define fi first

#define se second

#define Nmax 500005

const long double PI = acos(-1);



char mat[1003][1003];

int n,m,mn[1003][1003],ans;

queue<pii>H;

int dx[] = {0,1,-1,0};

int dy[] = {1,0,0,-1};



bool OK(int x, int y){

    if (x <= n && x >= 1 && y <= m && y >= 1) return 1;

    return 0;

}



int main(){

    ios::sync_with_stdio(false);

    cin >> n >> m;

    memset(mn,0xff,sizeof(mn));

    for (int i=1;i<=n;i++){

        cin >> mat[i]+1;

        for (int j=1;j<=m;j++){

            if (mat[i][j] == '#'){

                H.push({i,j});

                mn[i][j] = 0;

            }

        }

    }



    while (!H.empty()){

        pii crt = H.front();

        H.pop();



        for (int i=0;i<4;i++){

                int X = crt.first + dx[i];

                int Y = crt.second + dy[i];

                if (OK(X,Y) && mn[X][Y] == -1){

                    mn[X][Y] = mn[crt.first][crt.second] + 1;

                    ans = max(ans, mn[X][Y]);

                    H.push({X,Y});

                }

        }

    }



    cout << ans << '\n';



    return 0;

}