// includes
#include <bits/stdc++.h>
using namespace std;

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define bit(n) (1LL<<(n))
// functions
template <class T>bool chmax(T &a, const T &b){if(a < b){a = b; return 1;} return 0;}
template <class T>bool chmin(T &a, const T &b){if(a > b){a = b; return 1;} return 0;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << p.first << " " << p.second; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io{
  fast_io(){ios_base::sync_with_stdio(false); cin.tie(0); cout << fixed << setprecision(20);}
} fast_io_;

template <typename T>
struct edge{int from, to; T cost;};

template <typename T>
struct Graph{
  int n;
  vector<T> d;
  vector<edge<T>> es;
  Graph(int n): n(n){
    d.resize(n, numeric_limits<T>::max());
  }
  void adde(int from, int to, T cost){
    adde(edge<T>{from, to, cost});
  }
  void adde(edge<T> e){
    es.push_back(e);
  }
  bool bellman_ford(int s){
    T maxim = numeric_limits<T>::max();
    fill(d.begin(), d.end(), maxim);
    d[s] = 0;
    for(int i = 0; i < n; i++){
      bool update = false;
      for(auto e: es){
        if(d[e.from] != maxim && d[e.to] > d[e.from] + e.cost){
          d[e.to] = d[e.from] + e.cost;
          update = true;
          if(i == n - 1)return false;
        }
      }
      if(!update)break;
    }
    return true;
  }
};

using GraphL = Graph<ll>;
using GraphI = Graph<int>;




string s[300];

int main(int argc, char const* argv[])
{
  int n; cin >> n;
  rep(i, n)cin >> s[i];
  GraphI g(n);
  rep(i, n){
    rep(j, n){
      if(s[i][j] == '1'){
        g.adde(i, j, 1);
      }
    }
  }
  int res = -inf;
  rep(i, n){
    vector<bool> used(n, false);
    g.bellman_ford(i);
    int tmp = 0;
    bool ok = true;
    rep(j, n){
      rep(k, n){
        if(s[j][k] == '1'){
          if(g.d[j] == g.d[k])ok = false;
        }
      }
    }
    if(ok){
      rep(j, n){
        tmp = max(tmp, g.d[j]);
      }
      res = max(res, tmp + 1);
    }
  }
  if(res == -inf)cout << -1 << endl;
  else cout << res << endl;
  return 0;
}


Measured memory_bytes: 1276