import java.util.*;
import java.io.*;
 
public class Main {
    static ArrayList<ArrayList<Integer>> g;
    static int[] depth;
    static boolean flg = false;
    public static void main(String[] args) throws Exception {
        FastScanner sc = new FastScanner(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        StringBuilder sb = new StringBuilder();
        int n = sc.nextInt();
        g = new ArrayList<>();
        for(int i = 0; i < n; i++){
            g.add(new ArrayList<>());
        }
        int[][] dist = new int[n][n];
        for(int i = 0; i < n; i++){
            Arrays.fill(dist[i],Integer.MAX_VALUE/2);
        }
        depth = new int[n];
        for(int i = 0; i < n; i++){
            char[] s = sc.next().toCharArray();
            int j = 0;
            for(char c : s){
                int d = c-'0';
                if(d != 0) {
                    g.get(i).add(j);
                    dist[i][j] = 1;
                }
                j++;
            }
        }
        Arrays.fill(depth,-1);
        dfs(0,0);
        if(flg){
            pw.println(-1);
        }else{
            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]);
                    }
                }
            }
            int ans = 0;
            for(int i = 0; i < n; i++){
                for(int j = 0; j < n; j++){
                    if(i == j) continue;
                    ans = Math.max(ans,dist[i][j]);
                }
            }
            pw.println(ans+1);
        }
        pw.flush();
    }
    
    static void dfs(int pos, int dep){
        if(depth[pos] >= 0) {
            if(depth[pos] != dep) flg = true;
            return;
        }
        depth[pos] = dep;
        for(int x : g.get(pos)){
            dfs(x,dep^1);
        }
    }

    static class GeekInteger {
        public static void save_sort(int[] array) {
            shuffle(array);
            Arrays.sort(array);
        }
 
        public static int[] shuffle(int[] array) {
            int n = array.length;
            Random random = new Random();
            for (int i = 0, j; i < n; i++) {
                j = i + random.nextInt(n - i);
                int randomElement = array[j];
                array[j] = array[i];
                array[i] = randomElement;
            }
            return array;
        }
 
    }
}

class FastScanner {
    private BufferedReader reader = null;
    private StringTokenizer tokenizer = null;
    public FastScanner(InputStream in) {
        reader = new BufferedReader(new InputStreamReader(in));
        tokenizer = null;
    }

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

    public String nextLine() {
        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                return reader.readLine();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken("\n");
    }

    public long nextLong() {
        return Long.parseLong(next());
    }

    public int nextInt() {
        return Integer.parseInt(next());
    }

    public double nextDouble() {
         return Double.parseDouble(next());
    }
    
    public String[] nextArray(int n) {
        String[] a = new String[n];
        for (int i = 0; i < n; i++)
            a[i] = next();
        return a;
    }

    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;
    } 
}


Measured memory_bytes: 27824