package no402;

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.NoSuchElementException;
import java.util.Queue;

public class Main {
	public static int[] DI = {0,-1,-1,-1,0,1,1,1};
	public static int[] DJ = {1,1,0,-1,-1,-1,0,1};
	public static void main(String[] args) {
		IO io = new IO();
		int h = io.nextInt();
		int w = io.nextInt();
		char[][] m = new char[h+2][w+2];
		for(int i=0;i<=h+1;i++) {
			Arrays.fill(m[i], '.');
		}
		for(int i=0;i<h;i++) {
			String s = io.next();
			for(int j=0;j<w;j++) {
				m[i+1][j+1] = s.charAt(j);
			}
		}
		int h2 = h + 2;
		int w2 = w + 2;
		int[][] dist = new int[h2][w2];
		for(int i=0;i<h2;i++) {
			Arrays.fill(dist[i], 1 << 29);
		}
		Queue<Integer> q = new ArrayDeque<>();
		for(int i=0;i<h2;i++) {
			for(int j=0;j<w2;j++) {
				if (m[i][j] == '.') {
					dist[i][j] = 0;
					q.offer(i * 10000 + j);
				}
			}
		}
		while(!q.isEmpty()) {
			int c = q.poll();
			int ci = c / 10000;
			int cj = c % 10000;
			for(int k=0;k<8;k++) {
				int ni = ci + DI[k];
				int nj = cj + DJ[k];
				if (ni < 0 || ni >= h2 || nj < 0 || nj >= w2 || dist[ni][nj] <= dist[ci][cj] + 1) {
					continue;
				}
				dist[ni][nj] = dist[ci][cj] + 1;
				q.offer(ni * 10000 + nj);
			}
		}
//		System.out.println(Arrays.deepToString(dist));
		int ans = 0;
		for(int i=0;i<h2;i++) {
			for(int j=0;j<w2;j++) {
				ans = Math.max(ans,dist[i][j]);
			}
		}
		System.out.println(ans);
	}

	
}
class IO extends PrintWriter {
	private final InputStream in;
	private final byte[] buffer = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;
	
	public IO() { this(System.in);}
	public IO(InputStream source) { super(System.out); this.in = source;}
	private boolean hasNextByte() {
		if (ptr < buflen) {
			return true;
		}else{
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		}
		return true;
	}
	private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
	private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
	private static boolean isNewLine(int c) { return c == '\n' || c == '\r';}
	public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();}
	public boolean hasNextLine() { while(hasNextByte() && isNewLine(buffer[ptr])) ptr++; return hasNextByte();}
	public String next() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while(isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	public char[] nextCharArray(int len) {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		char[] s = new char[len];
		int i = 0;
		int b = readByte();
		while(isPrintableChar(b)) {
			if (i == len) {
				throw new InputMismatchException();
			}
			s[i++] = (char) b;
			b = readByte();
		}
		return s;
	}
	public String nextLine() {
		if (!hasNextLine()) {
			throw new NoSuchElementException();
		}
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while(!isNewLine(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	public long nextLong() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while(true){
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			}else if(b == -1 || !isPrintableChar(b)){
				return minus ? -n : n;
			}else{
				throw new NumberFormatException();
			}
			b = readByte();
		}
	}
	public int nextInt() {
		long nl = nextLong();
		if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) {
			throw new NumberFormatException();
		}
		return (int) nl;
	}
	public char nextChar() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		return (char) readByte();
	}
	public double nextDouble() { return Double.parseDouble(next());}
	public int[] nextIntArray(int n) { int[] a = new int[n]; for(int i=0;i<n;i++) a[i] = nextInt(); return a;}
	public long[] nextLongArray(int n) { long[] a = new long[n]; for(int i=0;i<n;i++) a[i] = nextLong(); return a;}
	public double[] nextDoubleArray(int n) { double[] a = new double[n]; for(int i=0;i<n;i++) a[i] = nextDouble(); return a;}
	public void nextIntArrays(int[]... a) { for(int i=0;i<a[0].length;i++) for(int j=0;j<a.length;j++) a[j][i] = nextInt();}
	public int[][] nextIntMatrix(int n,int m) { int[][] a = new int[n][]; for(int i=0;i<n;i++) a[i] = nextIntArray(m); return a;}
	public char[][] nextCharMap(int n,int m) { char[][] a = new char[n][]; for(int i=0;i<n;i++) a[i] = nextCharArray(m); return a;}
	public void close() { super.close(); try {in.close();} catch (IOException e) {}}
}