#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    int h, w;
    cin >> h >> w;
    string s[h+2];
    rep(i,h+2){
        if(i == 0 || i == h + 1){
            rep(j,w+2)s[i] += '.';
        }else{
            string ss; cin >> ss;
            s[i] = '.' + ss + '.';
        }
    }

    int f[h+2][w+2];
    rep(i,h+2){
        rep(j,w+2){
            if(i == 0 || j == 0 || i == h+1 || j == w+1){
                f[i][j] = 0;
            }else{
                f[i][j] = 1001001;
            }
            
        }
    }

    queue<P> que;
    srep(i,1,h+1){
        srep(j,1,w+1){
            if(s[i][j] == '.'){
                f[i][j] = 0;
                que.push(P(i,j));
            }else{
                if(i == 1 || i == h || j == 1 || j == w){
                    f[i][j] = 1;
                    que.push(P(i,j));
                }
            }
        }
    }

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

    while(que.size()){
        int x = que.front().first;
        int y = que.front().second;
        que.pop();
        rep(k,4){
            if(f[x+dx[k]][y+dy[k]] > f[x][y] + 1){
                f[x+dx[k]][y+dy[k]] = f[x][y] + 1;
                que.push(P(x+dx[k], y+dy[k]));
            }
        }
    }

    int ans = 0;

    rep(i,h+2)rep(j,w+2)ans = max(ans, f[i][j]);

    cout << ans << endl;
    return 0;
}