#![allow(unused_imports, unused_macros, non_snake_case)]
use std::cmp::{max, min, Ordering};
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};

//{{{ macros missing in 1.15.1
#[macro_use]
mod macros {
    macro_rules! eprint {
        ($($t:tt)*) => {{
            use ::std::io::Write;
            let _ = write!(::std::io::stderr(), $($t)*);
        }};
    }
    macro_rules! eprintln {
        () => { eprintln!(""); };
        ($($t:tt)*) => {{
            use ::std::io::Write;
            let _ = writeln!(::std::io::stderr(), $($t)*);
        }};
    }
    macro_rules! dbg {
        ($val:expr) => {
            match $val {
                tmp => {
                    eprintln!(
                        "[{}:{}] {} = {:#?}",
                        file!(),
                        line!(),
                        stringify!($val),
                        &tmp
                    );
                    tmp
                }
            }
        };
    }
}
//}}}

fn run() {
    let stdin = std::io::stdin();
    let mut sc = Scanner::new(stdin.lock());
    let n: usize = sc.read();
    let mut v = Vec::new();
    for i in 0..n {
        v.push(sc.read_chars());
    }
    let max = 1000_000_000;
    let mut d = vec![vec![max; n]; n];
    for i in 0..n {
        d[i][i] = 0;
    }
    for i in 0..n {
        for j in 0..n {
            if v[i][j] == '1' {
                d[i][j] = 1;
            }
        }
    }
    for k in 0..n {
        for i in 0..n {
            for j in 0..n {
                d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
            }
        }
    }
    let mut answer = 0;
    for s in 0..n {
        let mut map = HashMap::new();
        for i in 0..n {
            map.entry(&d[s][i]).or_insert_with(Vec::new).push(i);
        }
        let ans = map.len();
        let mut ok = true;
        for (_, v) in map {
            for &x in &v {
                for &y in &v {
                    if x != y && d[x][y] == 1 {
                        ok = false;
                    }
                }
            }
        }
        if ok && ans > answer {
            answer = ans;
        }
    }
    println!(
        "{}",
        if answer == 0 {
            "-1".to_string()
        } else {
            answer.to_string()
        }
    );
}

fn main() {
    std::thread::Builder::new()
        .name("run".to_string())
        .stack_size(1024 * 1024 * 1024)
        .spawn(run)
        .unwrap()
        .join()
        .unwrap()
}

//{{{ Scanner
pub struct Scanner<R> {
    reader: R,
}

impl<R> Scanner<R> {
    pub fn new(r: R) -> Scanner<R> {
        Scanner { reader: r }
    }
}

fn is_whitespace(b: u8) -> bool {
    b == b' ' || b == b'\n' || b == b'\r' || b == b'\t'
}

impl<R: std::io::Read> Scanner<R> {
    pub fn read<T: std::str::FromStr>(&mut self) -> T {
        let buf = std::io::Read::bytes(self.reader.by_ref())
            .map(|b| b.expect("Read failed"))
            .skip_while(|&b| is_whitespace(b))
            .take_while(|&b| !is_whitespace(b))
            .collect::<Vec<_>>();
        unsafe { std::str::from_utf8_unchecked(&buf) }
            .parse()
            .ok()
            .expect("Parse error")
    }

    pub fn read_vec<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read()).collect()
    }

    pub fn read_chars(&mut self) -> Vec<char> {
        self.read::<String>().chars().collect()
    }
}
//}}}


Measured memory_bytes: 8572