import java.io.PrintWriter;
import java.util.LinkedList;
import java.util.Scanner;

public class Main {
    static Scanner scan = new Scanner(System.in);
    static PrintWriter out = new PrintWriter(System.out);

    static int H, W;
    static char[][] map;
    static int [][] ansMap;
    static int ans = 0;
    
    public static void main(String[] args) {
        String line = scan.nextLine();
        String values[] = line.split(" ");
        H = Integer.parseInt(values[0]);
        W = Integer.parseInt(values[1]);;
        LinkedList<Point> q = new LinkedList<>();
        
        map = new char[H+2][W+2];
        ansMap = new int[H+2][W+2];
        
        for(int i=0; i<map.length; i++) {
            for(int j=0; j<map[0].length; j++) {
                if(i==0 || i==map.length-1 || j==0 || j==map[0].length-1) { 
                    map[i][j] = '.';
                    q.add(new Point(j, i));
                }
            }
        }
        
        for(int i=0; i<H; i++) {
            line = scan.nextLine();
            for(int j=0; j<W; j++) {
                map[i+1][j+1] = line.charAt(j);
                if(map[i+1][j+1] == '.') {
                    q.add(new Point(j+1,i+1));
                }
            }
        }
        
        int[] dx = {-1, 0, 1, -1, 1, -1, 0, 1};
        int[] dy = {-1, -1, -1, 0, 0, 1, 1, 1};
        
        while(!q.isEmpty()) {
            
            Point now = q.poll();
            
            for(int i=0; i<dx.length; i++) {
                int nextX = now.x + dx[i];
                int nextY = now.y + dy[i];
                
                if(nextX >= 0 && nextX < map[0].length && nextY >= 0 && nextY < map.length) {
                    if(map[nextY][nextX] == '#' && ansMap[nextY][nextX] == 0) {
                        ansMap[nextY][nextX] = ansMap[now.y][now.x] + 1;
                        q.add(new Point(nextX, nextY));
                        ans = Math.max(ans, ansMap[nextY][nextX]);
                    }
                }
            }
            
        }
        System.out.println(ans);
    }
    
    static void out() {
        for(int i=0; i<map.length; i++) {
            for(int j=0; j<map[0].length; j++) {
                System.out.print(map[i][j]);
            }
            System.out.println();
        }
    }
    
    static class Point {
        int x, y;
        Point(int x, int y) {
            this.x = x;
            this.y = y;
        }
    }
}