import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int h = sc.nextInt();
        int w = sc.nextInt();
        char[][] field = new char[h][];
        for (int i = 0; i < h; i++) {
            field[i] = sc.next().toCharArray();
        }
        int[][] dists = new int[h + 2][w + 2];
        for (int i = 0; i < h + 2; i++) {
            if (i >= 1 && i <= h) {
                Arrays.fill(dists[i], Integer.MAX_VALUE);
                dists[i][0] = 0;
                dists[i][w + 1] = 0;
                for (int j = 0; j < w; j++) {
                    if (field[i - 1][j] == '.') {
                        dists[i][j + 1] = 0;
                    }
                }
            }
        }
        for (int i = 1; i <= h; i++) {
            for (int j = 1; j <= w; j++) {
                int min = Math.min(dists[i][j - 1], Math.min(dists[i - 1][j - 1], dists[i - 1][j]));
                dists[i][j] = Math.min(dists[i][j], min + 1);
            }
            for (int j = w; j>= 1; j--) {
                int min = Math.min(dists[i][j + 1], Math.min(dists[i - 1][j + 1], dists[i - 1][j]));
                dists[i][j] = Math.min(dists[i][j], min + 1);
            }
        }
        for (int i = h; i >= 1; i--) {
            for (int j = 1; j <= w; j++) {
                int min = Math.min(dists[i][j - 1], Math.min(dists[i + 1][j - 1], dists[i + 1][j]));
                dists[i][j] = Math.min(dists[i][j], min + 1);
            }
            for (int j = w; j>= 1; j--) {
                int min = Math.min(dists[i][j + 1], Math.min(dists[i + 1][j + 1], dists[i + 1][j]));
                dists[i][j] = Math.min(dists[i][j], min + 1);
            }
        }
        int ans = 0;
        for (int i = 1; i <= h; i++) {
            for (int j = 1; j <= w; j++) {
                ans = Math.max(ans, dists[i][j]);
            }
        }
        System.out.println(ans);
    }
}

class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}