#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <ctime>
#include <cstring>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <numeric>
#include <utility>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <unordered_map>
using namespace std;

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

template<class T> vector<T> make_vec(size_t a) { return vector<T>(a); }
template<class T, class... Ts> auto make_vec(size_t a, Ts... ts) {
  return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}
template<class T, class V>
typename enable_if<is_class<T>::value == 0>::type fill(T &t, const V &v) {
    t = v;
}
template<class T, class V>
typename enable_if<is_class<T>::value != 0>::type fill(T &t, const V &v){
    for (auto &e : t) fill(e, v);
}

#define COUT(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl
template<class T1, class T2> ostream& operator << (ostream &s, pair<T1,T2> P)
{ return s << '<' << P.first << ", " << P.second << '>'; }
template<class T> ostream& operator << (ostream &s, vector<T> P)
{ for (int i = 0; i < P.size(); ++i) { if (i > 0) { s << " "; } s << P[i]; } return s; }
template<class T> ostream& operator << (ostream &s, vector<vector<T> > P)
{ for (int i = 0; i < P.size(); ++i) { s << endl << P[i]; } return s << endl; }

#define EACH(i, s) for (__typeof__((s).begin()) i = (s).begin(); i != (s).end(); ++i)
template<class T> ostream& operator << (ostream &s, set<T> P)
{ EACH(it, P) { s << "<" << *it << "> "; } return s << endl; }
template<class T1, class T2> ostream& operator << (ostream &s, map<T1,T2> P)
{ EACH(it, P) { s << "<" << it->first << "->" << it->second << "> "; } return s << endl; }

int H, W;
vector<string> fi;

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    while (cin >> H >> W) {
        fi.resize(H);
        for (int i = 0; i < H; ++i) cin >> fi[i];

        vector<vector<int> > dist(H, vector<int>(W, -1));
        using pint = pair<int,int>;
        queue<pint> que;
        for (int i = 0; i < H; ++i) {
            for (int j = 0; j < W; ++j) {
                if (fi[i][j] == '#') {
                    dist[i][j] = 0;
                    que.push(pint(i, j));
                }
            }
        }
        while (!que.empty()) {
            auto cur = que.front();
            que.pop();
            for (int dir = 0; dir < 4; ++dir) {
                int nx = cur.first + dx[dir];
                int ny = cur.second + dy[dir];
                if (nx < 0 || nx >= H || ny < 0 || ny >= W) continue;
                if (dist[nx][ny] == -1) {
                    dist[nx][ny] = dist[cur.first][cur.second] + 1;
                    que.push(pint(nx, ny));
                }
            }
        }
        int res = 0;
        for (int i = 0; i < H; ++i) {
            for (int j = 0; j < W; ++j) {
                res = max(res, dist[i][j]);
            }
        }
        cout << res << endl;
    }
}


















Measured memory_bytes: 13456