Main.java

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

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author MaxHeap
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TravelDiaries solver = new TravelDiaries();
        solver.solve(1, in, out);
        out.close();
    }

    static class TravelDiaries {
        final int INF = (int) 1e9;

        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();
            int m = in.nextInt();
            int[][] dist = new int[n][m];
            int[][] g = new int[n][m];
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    g[i][j] = in.nextInt();
                }
            }
            for (int[] temp : dist) Arrays.fill(temp, INF);
            Queue<IntPair> q = new ArrayDeque<>();
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    if (g[i][j] == 2) {
                        q.add(new IntPair(i, j));
                        dist[i][j] = 0;
                    }
                }
            }

            int[] dx = {1, -1, 0, 0};
            int[] dy = {0, 0, 1, -1};
            while (!q.isEmpty()) {
                IntPair cur = q.poll();
                for (int i = 0; i < 4; i++) {
                    int xx = cur.getFirst() + dx[i];
                    int yy = cur.getSecond() + dy[i];
                    if (xx < 0 || yy < 0 || xx >= n || yy >= m || g[xx][yy] != 1) continue;
                    if (dist[xx][yy] > dist[cur.getFirst()][cur.getSecond()] + 1) {
                        dist[xx][yy] = dist[cur.getFirst()][cur.getSecond()] + 1;
                        q.add(new IntPair(xx, yy));
                    }
                }
            }

            int ans = 0;
            boolean isReachable = true;
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    if (dist[i][j] >= INF && g[i][j] == 1) isReachable = false;
                    if (dist[i][j] >= INF) continue;
                    ans = Math.max(ans, dist[i][j]);
                }
            }
            out.println(isReachable ? ans : -1);
        }

    }

    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {
            if (this.numChars == -1) {
                throw new InputMismatchException();
            } else {
                if (this.curChar >= this.numChars) {
                    this.curChar = 0;

                    try {
                        this.numChars = this.stream.read(this.buf);
                    } catch (IOException ex) {
                        throw new InputMismatchException();
                    }

                    if (this.numChars <= 0) {
                        return -1;
                    }
                }

                return this.buf[this.curChar++];
            }
        }

        public int nextInt() {
            int c;
            for (c = this.read(); isSpaceChar(c); c = this.read()) {
            }

            byte sgn = 1;
            if (c == 45) {
                sgn = -1;
                c = this.read();
            }

            int res = 0;

            while (c >= 48 && c <= 57) {
                res *= 10;
                res += c - 48;
                c = this.read();
                if (isSpaceChar(c)) {
                    return res * sgn;
                }
            }

            throw new InputMismatchException();
        }

        public static boolean isSpaceChar(int c) {
            return c == 32 || c == 10 || c == 13 || c == 9 || c == -1;
        }

    }

    static class IntPair implements Comparable<IntPair> {
        int first;
        int second;

        public IntPair(int first, int second) {
            this.first = first;
            this.second = second;
        }


        public int compareTo(IntPair a) {
            if (second == a.second) {
                return Integer.compare(first, a.first);
            }
            return Integer.compare(second, a.second);
        }


        public String toString() {
            return "<" + first + ", " + second + ">";
        }


        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;

            IntPair a = (IntPair) o;

            if (first != a.first) return false;
            return second == a.second;
        }


        public int hashCode() {
            int result = first;
            result = 31 * result + second;
            return result;
        }

        public int getFirst() {
            return first;
        }

        public int getSecond() {
            return second;
        }

    }
}