#include <bits/stdc++.h>
using namespace std;


/* macro */
#define rep(i,a,b) for(int i=a;i<b;i++)
#define revrep(i,a,b) for(int i = a; i > b; i--)
#define int long long
#define exist(s,e) ((s).find(e)!=(s).end())
#define all(v) (v).begin(), (v).end()
#define each(s,itr) for(auto (itr) = s.begin(); (itr) != s.end(); (itr)++)
#define sum(v) accumulate(all(v), (0LL))
#define sort(v) sort(all(v))



/* constant */
const int inf = 100100100100100100;
const int mod = 1000000007;
int dx[8]={1,0,-1,0,-1,1,-1,1};
int dy[8]={0,1,0,-1,-1,-1,1,1};


/* io_method */
int input(){int tmp;cin >> tmp;return tmp;}
string raw_input(){string tmp;cin >> tmp;return tmp;}
string readline(){string s;getline(cin, s);return s;}
template<class T> void printx(T n){cout << n;}
template<class T, class U> void printx(pair<T, U> p){cout << "(" << p.first << "," << p.second << ")";}
template<class T> void printx(vector<T> v){cout << "{";rep(i,0,v.size()){printx(v[i]);if(i != v.size()-1)printx(",");}cout << "}";}
template<class T> void print(T n){printx(n);cout << endl;}
template<class T> void print(set<T> s){cout << "{";each(s, e){if(e != s.begin()) printx(",");printx(*e);}cout << "}" << endl;}
template<class T, class U> void print(map<T, U> mp){cout << "{";each(mp, e){cout << "(" << e -> first << "," << e -> second << ")";}cout << "}" << endl;}


/* general_method */
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; }


/* math_library */
int ceil(int a, int b){if(a % b == 0){return a/b;}else{return a/b + 1;}}


/* main */


signed main(){

    cin.tie(0);
    ios::sync_with_stdio(false);

    int h, w; cin >> h >> w;

    int dp[h][w];
    rep(i,0,h){
        rep(j,0,w){
            char c; cin >> c;
            if(c == '.'){
                dp[i][j] = 0;
            }else{
                dp[i][j] = inf;
            }
        }
    }

    int tx[3] = {-1, 0, -1};
    int ty[3] = {0, -1, -1};

    rep(i,0,h){
        rep(j,0,w){
            rep(k,0,3){
                int x = j + tx[k];
                int y = i + ty[k];
                chmin(dp[i][j], (-1 < x && -1 < y ? dp[y][x] + 1 : 1));
            }
        }
    }

    int ans = 0;
    rep(i,0,h){
        rep(j,0,w){
            chmax(ans, dp[i][j]);
        }
    }

    print((ans + 1)/ 2);













   




}