using System;
using System.Linq;
using System.Collections.Generic;

namespace Contest
{
    class Program
    {
        static void Main(string[] args)
        {
            AGC039.B();
        }

        class AGC039
        {
            public static void A()
            {
                var S = Read.Str();
                var K = Read.Long();
                int count0 = 0;
                bool lastMod0 = false;
                for(int i = 1; i < S.Length; ++i)
                {
                    if (S[i] == S[i - 1])
                    {
                        count0++;
                        if (i == S.Length - 1) { lastMod0 = true; }
                        i++;
                    }
                }
                if (S[0] != S.Last() || lastMod0) { Console.WriteLine(K * count0); return; }
                int count1 = 1;
                bool lastMod1 = false;
                for (int i = 2; i < S.Length; ++i)
                {
                    if (S[i] == S[i - 1])
                    {
                        count1++;
                        if (i == S.Length - 1) { lastMod1 = true; }
                        i++;
                    }
                }
                if (lastMod1)
                {
                    Console.WriteLine((K + 1) / 2 * count0 + K / 2 * count1);
                }
                else
                {
                    Console.WriteLine(count0 + (K - 1) * count1);
                }
            }
            public static void B()
            {
                var N = Read.Int();
                long[,] dist = new long[N, N];
                for(int i = 0; i < N; ++i)
                {
                    var S = Read.Str();
                    for(int j = 0; j < N; ++j)
                    {
                        dist[i, j] = i == j ? 0 : (S[j] == '1' ? 1 : 1000000);
                    }
                }
                var wf = Util.Dup(dist);
                Util.WarshallFloyd(wf);
                List<int> even = new List<int>();
                List<int> odd = new List<int>();
                for(int i = 0; i < N; ++i)
                {
                    (wf[0, i] % 2 == 0 ? even : odd).Add(i);
                }
                for (int i = 0; i < even.Count; ++i)
                {
                    for (int j = i + 1; j < even.Count; ++j)
                    {
                        if (dist[even[i], even[j]] == 1) { Console.WriteLine(-1); return; }
                    }
                }
                for (int i = 0; i < odd.Count; ++i)
                {
                    for (int j = i + 1; j < odd.Count; ++j)
                    {
                        if (dist[odd[i], odd[j]] == 1) { Console.WriteLine(-1); return; }
                    }
                }
                long max = 0;
                for(int i = 0; i < N; ++i)
                {
                    for(int j = 0; j < N; ++j)
                    {
                        max = Math.Max(max, wf[i, j]);
                    }
                }
                Console.WriteLine(max + 1);
            }
        }



        class Util
        {
            public static T[,] Dup<T>(T[,] matrix)
            {
                var n0 = matrix.GetLength(0);
                var n1 = matrix.GetLength(1);
                var m = new T[n0, n1];
                for(int i = 0; i < n0; ++i)
                {
                    for(int j = 0; j < n1; ++j)
                    {
                        m[i, j] = matrix[i, j];
                    }
                }
                return m;
            }
            public static void WarshallFloyd(long[,] dist)
            {
                var N = dist.GetLength(0);
                for(int k = 0; k < N; ++k)
                {
                    for(int i = 0; i < N; ++i)
                    {
                        for(int j = 0; j < N; ++j)
                        {
                            dist[i, j] = Math.Min(dist[i, j], dist[i, k] + dist[k, j]);
                        }
                    }
                }
            }
        }


        static class Read
        {
            static Queue<string> queue = new Queue<string>();
            static void Enqueue() { var ss = Console.ReadLine().Split(' '); foreach (var s in ss) { queue.Enqueue(s); } }
            public static int Int() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt32(queue.Dequeue()); }
            public static long Long() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt64(queue.Dequeue()); }
            public static string Str() { if (queue.Count == 0) { Enqueue(); } return queue.Dequeue(); }
            public static int[] IntN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt32(s)).ToArray(); }
            public static long[] LongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt64(s)).ToArray(); }
            public static string[] StrN() { return Console.ReadLine().Split(' '); }
            public static Tuple<int, int>[] TupleInt(int n) { List<Tuple<int, int>> list = new List<Tuple<int, int>>(); for (int i = 0; i < n; ++i) { var ab = Read.IntN(); list.Add(new Tuple<int, int>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<long, long>[] TupleLong(int n) { List<Tuple<long, long>> list = new List<Tuple<long, long>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<long, long>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<string, string>[] TupleStr(int n) { List<Tuple<string, string>> list = new List<Tuple<string, string>>(); for (int i = 0; i < n; ++i) { var ab = Read.StrN(); list.Add(new Tuple<string, string>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<double, double>[] TupleDouble(int n) { List<Tuple<double, double>> list = new List<Tuple<double, double>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<double, double>(ab[0], ab[1])); } return list.ToArray(); }
            public static long[,] LongMatrix(int r, int c)
            {
                var mat = new long[r, c];
                for (int i = 0; i < r; ++i)
                {
                    var x = Read.LongN();
                    for (int j = 0; j < c; ++j)
                    {
                        mat[i, j] = x[j];
                    }
                }
                return mat;
            }
            public static Dictionary<int, HashSet<int>> AdjacencyList(int N, int M)
            {
                Dictionary<int, HashSet<int>> dict = new Dictionary<int, HashSet<int>>();
                for (int i = 0; i <= N; ++i)
                {
                    dict.Add(i, new HashSet<int>());
                }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN();
                    dict[ab[0]].Add(ab[1]);
                    dict[ab[1]].Add(ab[0]);
                }
                return dict;
            }
            public static Dictionary<int, Dictionary<int, long>> AdjacencyListWithWeight(int N, int M)
            {
                Dictionary<int, Dictionary<int, long>> dict = new Dictionary<int, Dictionary<int, long>>();
                for (int i = 0; i <= N; ++i)
                {
                    dict.Add(i, new Dictionary<int, long>());
                }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN();
                    dict[ab[0]].Add(ab[1], ab[2]);
                    dict[ab[1]].Add(ab[0], ab[2]);
                }
                return dict;
            }
        }
    }
}


Measured memory_bytes: 13792