import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.List;

public class Main {
	static StringBuilder out = new StringBuilder();
	static String ls = System.lineSeparator();
	static final String OK = "Possible";
	static final String NG = "Impossible";
	static FastReader fr = new FastReader();

	// static final int INF = Integer.MAX_VALUE - 300000000;

	public static void main(String[] args) throws Exception, IOException {
		char wall = '#';
		char hole = '.';

		int w = fr.nextInt();
		int h = fr.nextInt();
		char[][] space = new char[h][w];
		for (int i = 0; i < h; i++) {
			space[i] = fr.next().toCharArray();
		}

		List<int[]> all = new ArrayList<>();
		List<int[]> one = new ArrayList<>();

		for (int i = 0; i < h; i++)
			for (int j = 0; j < w; j++)
				if (space[i][j] == hole) {
					int[] a = { i, j };
					all.add(a);
				}

		one.add(all.get(0));
		int i = 0;
		for (;;) {
			int preSize = one.size();
			all.removeAll(one);
			for (; i < preSize; i++) {
				int[] a = one.get(i);
				for (int[] b : all) {
					if (Math.abs(a[0] - b[0]) + Math.abs(a[1] - b[1]) == 1) {
						one.add(b);
					}
				}
			}
			if(preSize == one.size())
				break;
		}

		all.removeAll(one);
		List<int[]> two = all;

		int min = Integer.MAX_VALUE;
		for(int[] a : one){
			for(int[] b : two){
				int range = Math.abs(a[0] - b[0]) + Math.abs(a[1] - b[1]);
				if(range < min)
					min = range;
			}
		}

		System.out.println(min - 1);
	}

	static void printExit(String msg) {
		System.out.println(msg);
		System.exit(0);
	}
}

class FastReader {
	private InputStream in = System.in;
	private byte[] buf = new byte[1024];
	private int charNum;
	private int charLen;
	private StringBuilder sb = new StringBuilder();

	public int read() {
		if (charLen == -1)
			throw new InputMismatchException();
		if (charNum >= charLen) {
			charNum = 0;
			try {
				charLen = in.read(buf);
			} catch (IOException e) {
				throw new InputMismatchException();
			}
			if (charLen <= 0)
				return -1;
		}
		return buf[charNum++];
	}

	public String next() {
		int c = read();
		while (isWhitespace(c)) {
			c = read();
		}
		sb.setLength(0);
		do {
			sb.appendCodePoint(c);
			c = read();
		} while (!isWhitespace(c));
		return sb.toString();
	}

	public char[] nextCharArray() {
		return next().toCharArray();
	}

	public int nextInt() {
		return (int) nextLong();
	}

	public int[] nextIntArray(int n) {
		int[] array = new int[n];
		for (int i = 0; i < n; i++)
			array[i] = nextInt();
		return array;
	}

	public List<Integer> nextIntList(int n) {
		Integer[] array = new Integer[n];
		for (int i = 0; i < n; i++)
			array[i] = nextInt();
		return Arrays.asList(array);
	}

	public int[][] nextIntArray2D(int n, int m) {
		int[][] array = new int[n][m];
		for (int i = 0; i < n; i++)
			array[i] = nextIntArray(m);
		return array;
	}

	public List<int[]> nextIntsList(int n, int m) {
		List<int[]> list = new ArrayList<>(n);
		for (int i = 0; i < n; i++)
			list.add(nextIntArray(m));
		return list;
	}

	public long nextLong() {
		int c = read();
		while (isWhitespace(c)) {
			c = read();
		}
		int sgn = 1;
		if (c == '-') {
			sgn = -1;
			c = read();
		}
		long res = 0;
		do {
			if (c < '0' || c > '9')
				throw new InputMismatchException();
			res *= 10;
			res += c - '0';
			c = read();
		} while (!isWhitespace(c));
		return res * sgn;
	}

	public double nextDouble() {
		return Double.parseDouble(next());
	}

	public double[] nextDoubleArray(int n) {
		double[] array = new double[n];
		for (int i = 0; i < n; i++)
			array[i] = nextDouble();
		return array;
	}

	public boolean isWhitespace(int c) {
		return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
	}
}