#[allow(unused_imports)]
use std::cmp::*;
#[allow(unused_imports)]
use std::collections::*;
#[allow(unused_imports)]
use std::ops::*;
#[allow(unused_imports)]
use std::io::{Write, BufWriter};

// https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
macro_rules! input {
    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}

macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

    ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };
}

macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

    ($next:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, [ $t:tt ]) => {{
        let len = read_value!($next, usize);
        (0..len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    }};

    ($next:expr, $t:ty) => {
        $next().parse::<$t>().expect("Parse error")
    };
}

struct Tuple {
    p: usize,
    cur: usize,
    d: i32,
}

impl Tuple {
    fn new(p: usize, cur: usize, d: i32) -> Tuple {
        Tuple{
            p: p,
            cur: cur,
            d: d,
        }
    }   
}

fn solve() {
    input! {
        n: usize,
        board: [chars; n],
    }
    let mut edge: Vec<Vec<usize>> = vec![vec![]; n];
    for i in 0..n {
        for j in 0..n {
            if board[i][j] == '0' {
                continue;
            }
            edge[i].push(j);
            edge[j].push(i);
        }
    }
    let mut q: VecDeque<Tuple> = VecDeque::new();
    let mut ans = -1;
    for i in 0..n {
        let t = Tuple::new(n,i,1);
        q.push_back(t);
        let mut seen = vec![false; n];
        let mut depth = vec![-1;n];
        seen[i] = true;
        depth[i] = 1;
        let mut max_depth = 0;
        while let Some(Tuple{p,cur,d}) = q.pop_front() {
            max_depth = max(depth[cur], max_depth);
            for &j in &edge[cur] {
                if seen[j] {
                    if (depth[j]+depth[cur])%2==0 {
                        max_depth = -1;
                        break;
                    }
                    continue;
                }
                q.push_back(Tuple::new(cur,j,d+1));
                seen[j] = true;
                depth[j] = d+1;
            }
            if max_depth==-1 {break;}
        }
        ans = max(ans, max_depth);
    }
    println!("{}", ans);
}

fn main() {
    // In order to avoid potential stack overflow, spawn a new thread.
    let stack_size = 104_857_600; // 100 MB
    let thd = std::thread::Builder::new().stack_size(stack_size);
    thd.spawn(|| solve()).unwrap().join().unwrap();
}


Measured memory_bytes: 10620