#include <algorithm>
#include <atcoder/all>
#include <bitset>
#include <cassert>
#include <cmath>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvb vector<vector<bool>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int, int>>
#define vpll vector<pair<ll, ll>>
#define vvpii vector<vector<pair<int, int>>>
#define vvpll vector<vector<pair<ll, ll>>>

template <typename T>
void debug(T e) {
    cerr << e << endl;
}

template <typename T>
void debug(vector<T> &v) {
    rep(i, v.size()) { cerr << v[i] << " "; }
    cerr << endl;
}

template <typename T>
void debug(vector<vector<T>> &v) {
    rep(i, v.size()) {
        rep(j, v[i].size()) { cerr << v[i][j] << " "; }
        cerr << endl;
    }
}

template <typename T>
void debug(vector<pair<T, T>> &v) {
    rep(i, v.size()) { cerr << v[i].first << " " << v[i].second << endl; }
}

template <typename T>
void debug(set<T> &st) {
    for (auto itr = st.begin(); itr != st.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(multiset<T> &ms) {
    for (auto itr = ms.begin(); itr != ms.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(map<T, T> &mp) {
    for (auto itr = mp.begin(); itr != mp.end(); itr++) {
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out() { cerr << endl; }

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

using mint = modint998244353;

void debug_mint1(vector<mint> &vec) {
    for (int i = 0; i < vec.size(); i++) {
        cerr << vec[i].val() << " ";
    }
    cerr << endl;
}

void debug_mint2(vector<vector<mint>> &vec) {
    for (int i = 0; i < vec.size(); i++) {
        for (int j = 0; j < vec[i].size(); j++) {
            cerr << vec[i][j].val() << " ";
        }
        cerr << endl;
    }
}

int main() {
    ll H, W;
    cin >> H >> W;
    vector<string> S(H);
    rep(i, H) cin >> S[i];

    // BFS
    ll INF = 1000000000023LL;
    vector<vector<ll>> dist(H, vector<ll>(W, INF));
    queue<pll> que;
    for (ll i = 0; i < H; i++){
        if (S[i][0] == '#'){
            dist[i][0] = 1;
            que.push(make_pair(i, 0));
        }
        if (S[i][W - 1] == '#'){
            if (dist[i][W - 1] < INF) continue;
            dist[i][W - 1] = 1;
            que.push(make_pair(i, W - 1));
        }
    }
    for (ll j = 0; j < W; j++){
        if (S[0][j] == '#'){
            if (dist[0][j] < INF) continue;
            dist[0][j] = 1;
            que.push(make_pair(0, j));
        }
        if (S[H - 1][j] == '#'){
            if (dist[H - 1][j] < INF) continue;
            dist[H - 1][j] = 1;
            que.push(make_pair(H - 1, j));
        }
    }
    vector<ll> dx = {1, 1, 0, -1, -1, -1, 0, 1};
    vector<ll> dy = {0, 1, 1, 1, 0, -1, -1, -1};

    for (ll i = 0; i < H; i++){
        for (ll j = 0; j < W; j++){
            if (S[i][j] == '.'){
                for (ll k = 0; k < 8; k++){
                    ll nx = i + dx[k];
                    ll ny = j + dy[k];
                    if (nx >= 0 && nx < H && ny >= 0 && ny < W){
                        if (S[nx][ny] == '#'){
                            if (dist[nx][ny] == INF){
                                dist[nx][ny] = 1;
                                que.push(make_pair(nx, ny));
                            }
                        }
                    }
                }
            }
        }
    }
    while (que.size()){
        pll p = que.front();
        que.pop();
        ll px = p.first;
        ll py = p.second;
        for (ll k = 0; k < 8; k++){
            ll nx = px + dx[k];
            ll ny = py + dy[k];
            if (nx >= 0 && nx < H && ny >= 0 && ny < W){
                if (S[nx][ny] == '#'){
                    if (dist[nx][ny] == INF){
                        dist[nx][ny] = dist[px][py] + 1;
                        que.push(make_pair(nx, ny));
                    }
                }
            }
        }
    }
    // debug(dist);
    ll ans = 0;
    rep(i, H){
        rep(j, W){
            if (dist[i][j] != INF){
                ans = max(ans, dist[i][j]);
            }
        }
    }
    cout << ans << endl;
}