#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<numeric>
#include<cmath>
#include<utility>
#include<tuple>
#include<cstdint>
#include<cstdio>
#include<iomanip>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<deque>
#include<unordered_map>
#include<unordered_set>
#include<bitset>
#include<cctype>
#include<chrono>
#include<random>
#include<cassert>
#include<cstddef>
#include<iterator>
#include<string_view>
#include<type_traits>

#ifdef LOCAL
#  include "debug_print.hpp"
#  define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define debug(...) (static_cast<void>(0))
#endif

using namespace std;
#define rep(i,n) for(int i=0; i<(n); i++)
#define rrep(i,n) for(int i=(n)-1; i>=0; i--)
#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 ALL(v) v.begin(), v.end()
#define RALL(v) v.rbegin(), v.rend()
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
#define pb push_back
using ll = long long;
using D = double;
using LD = long double;
using P = pair<int, int>;
template<typename T> using PQ = priority_queue<T,vector<T>>;
template<typename T> using minPQ = priority_queue<T, vector<T>, greater<T>>;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
void yesno(bool flag) {cout << (flag?"Yes":"No") << "\n";}

template<typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << p.first << " " << p.second;
    return os;
}
template<typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p) {
    is >> p.first >> p.second;
    return is;
}

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
    int s = (int)v.size();
    for (int i = 0; i < s; i++) os << (i ? " " : "") << v[i];
    return os;
}
template<typename T>
istream &operator>>(istream &is, vector<T> &v) {
    for (auto &x : v) is >> x;
    return is;
}
void in() {}
template<typename T, class... U>
void in(T &t, U &...u) {
    cin >> t;
    in(u...);
}
void out() { cout << "\n"; }
template<typename T, class... U, char sep = ' '>
void out(const T &t, const U &...u) {
    cout << t;
    if (sizeof...(u)) cout << sep;
    out(u...);
}
void outr() {}
template<typename T, class... U, char sep = ' '>
void outr(const T &t, const U &...u) {
    cout << t;
    outr(u...);
}

const int dx[8] = {1,1,0,-1,-1,-1,0,1};
const int dy[8] = {0,1,1,1,0,-1,-1,-1};

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int h,w; in(h,w);
    char s[h+2][w+2];
    rep(i,h+2)rep(j,w+2) s[i][j] = '.';
    rep(i,h)rep(j,w) in(s[i+1][j+1]);
    int dist[h+2][w+2];
    rep(i,h+2)rep(j,w+2) dist[i][j] = (s[i][j] == '.' ? 0 : -1);
    queue<P> q;
    rep(i,h+2)rep(j,w+2) if(s[i][j] == '.') q.push({i,j});
    while(q.size()){
        auto [x,y] = q.front(); q.pop();
        rep(i,8){
            int nx = x+dx[i];
            int ny = y+dy[i];
            if(nx < 0 || nx >= h+1 || ny < 0 || ny >= w+1) continue;
            if(dist[nx][ny] != -1)  continue;
            dist[nx][ny] = dist[x][y]+1;
            q.push({nx,ny});
        }
    }
    int ans = 0;
    rep(i,h+2)rep(j,w+2) chmax(ans, dist[i][j]);
        out(ans);
}