import java.io.PrintWriter;
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;
    
    public static void main(String[] args) {
        
        String line = scan.nextLine();
        String values[] = line.split(" ");
        H = Integer.parseInt(values[0]);
        W = Integer.parseInt(values[1]);;
        
        map = new char[H][W];
        ansMap = new int[H][W];
        
        for(int i=0; i<H; i++) {
            line = scan.nextLine();
            for(int j=0; j<W; j++) {
                map[i][j] = line.charAt(j);
                if(map[i][j] == '#') {
                    ansMap[i][j] = -1;
                }
                if((i==0 || i==W-1 || j==0 || j==H-1) && map[i][j] == '#') { 
                    ansMap[i][j] = 1;
                }
            }
        }
        
        int[] dx = {-1, 0, 1, -1, 1, -1, 0, 1};
        int[] dy = {-1, -1, -1, 0, 0, 1, 1, 1};
        
        for(int count=0; count<=1500; count++) {
            boolean find = false;
            
            for(int i=0; i<H; i++) {
                for(int j=0; j<W; j++) {
                    
                    if(ansMap[i][j] == count) {
                        for(int k=0; k<dx.length; k++) {
                            int nextX = j + dx[k];
                            int nextY = i + dy[k];
                            
                            if(nextX >= 0 && nextX < W && nextY >= 0 && nextY < H && ansMap[nextY][nextX] == -1) {
                                ansMap[nextY][nextX] = (count+1);
                                find = true;
                            }
                        }    
                    }
                }
            }
            if(find == false) {
                System.out.println(count==0? 1500 : count);
                break;
            }
        }
    }
}