import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.stream.IntStream;
import java.util.Arrays;
import java.util.OptionalInt;
import java.util.ArrayList;
import java.nio.charset.Charset;
import java.util.StringTokenizer;
import java.io.OutputStreamWriter;
import java.util.NoSuchElementException;
import java.io.OutputStream;
import java.io.BufferedWriter;
import java.util.Collection;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UncheckedIOException;
import java.util.List;
import java.io.Writer;
import java.util.Queue;
import java.io.BufferedReader;
import java.util.ArrayDeque;
import java.io.InputStream;

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

    static class BGraphPartition {
        public void solve(int testNumber, LightScanner in, LightWriter out) {
            // out.setBoolLabel(LightWriter.BoolLabel.YES_NO_FIRST_UP);
            int n = in.ints();
            char[][] b = new char[n][];
            for (int i = 0; i < n; i++) b[i] = in.string().toCharArray();
            BGraphPartition.Node[] nodes = new BGraphPartition.Node[n];
            for (int i = 0; i < n; i++) nodes[i] = new BGraphPartition.Node(i);
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < i; j++) {
                    if (b[i][j] == '1') {
                        nodes[i].adj.add(nodes[j]);
                        nodes[j].adj.add(nodes[i]);
                    }
                }
            }
            try {
                nodes[0].dfs(0);
            } catch (RuntimeException ignored) {
                out.ans(-1).ln();
                return;
            }

            int ans = 0;
            for (int i = 0; i < n; i++) {
                int[] distance = new int[n];
                Arrays.fill(distance, -1);
                Queue<BGraphPartition.Node> q = new ArrayDeque<>();
                distance[i] = 0;
                q.offer(nodes[i]);
                while (!q.isEmpty()) {
                    BGraphPartition.Node now = q.poll();
                    for (BGraphPartition.Node next : now.adj) {
                        if (distance[next.index] >= 0) continue;
                        distance[next.index] = distance[now.index] + 1;
                        q.offer(next);
                    }
                }
                ans = Math.max(ans, IntMath.max(distance));
            }
            out.ans(ans + 1).ln();
        }

        private static class Node {
            int index;
            List<BGraphPartition.Node> adj = new ArrayList<>();
            int parity = -1;

            Node(int index) {
                this.index = index;
            }

            void dfs(int par) {
                if (parity >= 0 && par != parity) throw new RuntimeException();
                if (parity >= 0) return;
                parity = par;
                for (BGraphPartition.Node next : adj) {
                    next.dfs(1 - par);
                }
            }

        }

    }

    static final class IntMath {
        private IntMath() {
        }

        public static int max(int... v) {
            return Arrays.stream(v).max().orElseThrow(NoSuchElementException::new);
        }

    }

    static class LightScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public LightScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
        }

        public String string() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new UncheckedIOException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int ints() {
            return Integer.parseInt(string());
        }

    }

    static class LightWriter implements AutoCloseable {
        private final Writer out;
        private boolean autoflush = false;
        private boolean breaked = true;

        public LightWriter(Writer out) {
            this.out = out;
        }

        public LightWriter(OutputStream out) {
            this(new BufferedWriter(new OutputStreamWriter(out, Charset.defaultCharset())));
        }

        public LightWriter print(char c) {
            try {
                out.write(c);
                breaked = false;
            } catch (IOException ex) {
                throw new UncheckedIOException(ex);
            }
            return this;
        }

        public LightWriter print(String s) {
            try {
                out.write(s, 0, s.length());
                breaked = false;
            } catch (IOException ex) {
                throw new UncheckedIOException(ex);
            }
            return this;
        }

        public LightWriter ans(String s) {
            if (!breaked) {
                print(' ');
            }
            return print(s);
        }

        public LightWriter ans(int i) {
            return ans(Integer.toString(i));
        }

        public LightWriter ln() {
            print(System.lineSeparator());
            breaked = true;
            if (autoflush) {
                try {
                    out.flush();
                } catch (IOException ex) {
                    throw new UncheckedIOException(ex);
                }
            }
            return this;
        }

        public void close() {
            try {
                out.close();
            } catch (IOException ex) {
                throw new UncheckedIOException(ex);
            }
        }

    }
}



Measured memory_bytes: 29008