#include <bits/stdc++.h>
#define LLI long long int
#define FOR(v, a, b) for(LLI v = (a); v < (b); ++v)
#define FORE(v, a, b) for(LLI v = (a); v <= (b); ++v)
#define REP(v, n) FOR(v, 0, n)
#define REPE(v, n) FORE(v, 0, n)
#define REV(v, a, b) for(LLI v = (a); v >= (b); --v)
#define ALL(x) (x).begin(), (x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define ITR(it, c) for(auto it = (c).begin(); it != (c).end(); ++it)
#define RITR(it, c) for(auto it = (c).rbegin(); it != (c).rend(); ++it)
#define EXIST(c,x) ((c).find(x) != (c).end())
#define fst first
#define snd second
#define popcount __builtin_popcount
#define UNIQ(v) (v).erase(unique(ALL(v)), (v).end())
#define bit(i) (1LL<<(i))

#ifdef DEBUG
#include <misc/C++/Debug.cpp>
#else
#define dump(...) ((void)0)
#endif

#define gcd __gcd

using namespace std;
template <class T> constexpr T lcm(T m, T n){return m/gcd(m,n)*n;}

template <typename I> void join(ostream &ost, I s, I t, string d=" "){for(auto i=s; i!=t; ++i){if(i!=s)ost<<d; ost<<*i;}ost<<endl;}
template <typename T> istream& operator>>(istream &is, vector<T> &v){for(auto &a : v) is >> a; return is;}

template <typename T, typename U> bool chmin(T &a, const U &b){return (a>b ? a=b, true : false);}
template <typename T, typename U> bool chmax(T &a, const U &b){return (a<b ? a=b, true : false);}
template <typename T, size_t N, typename U> void fill_array(T (&a)[N], const U &v){fill((U*)a, (U*)(a+N), v);}

struct Init{
  Init(){
    cin.tie(0);
    ios::sync_with_stdio(false);
  }
}init;

template <typename Cost = int> class Edge{
public:
  int from,to;
  Cost cost;
  Edge() {}
  Edge(int to, Cost cost): to(to), cost(cost){}
  Edge(int from, int to, Cost cost): from(from), to(to), cost(cost){}

  Edge rev() const {return Edge(to,from,cost);}
  
  friend ostream& operator<<(ostream &os, const Edge &e){
    os << "(FROM: " << e.from << "," << "TO: " << e.to << "," << "COST: " << e.cost << ")";
    return os;
  }
};

template <typename T> using Graph = vector<vector<Edge<T>>>;
template <typename T> using Tree = vector<vector<Edge<T>>>;

template <typename C, typename T> void add_edge(C &g, int from, int to, T w){
  g[from].push_back(Edge<T>(from, to, w));  
}

template <typename C, typename T> void add_undirected(C &g, int a, int b, T w){
  g[a].push_back(Edge<T>(a, b, w));
  g[b].push_back(Edge<T>(b, a, w));
}


template <typename T>
bool is_bipartite_graph(const Graph<T> &graph){
  vector<int> check(graph.size(), -1);
  vector<bool> visit(graph.size(), false);
  stack<int> st;

  st.push(0);
  check[0] = 0;

  while(!st.empty()){
    auto cur = st.top(); st.pop();
    if(visit[cur]) continue;
    visit[cur] = true;

    for(auto &e : graph[cur]){
      if(check[e.to] == check[e.from]) return false;

      if(check[e.to] == -1){
        check[e.to] = (check[e.from]==0 ? 1 : 0);
      }

      st.push(e.to);
    }
  }
  
  return true;
}


int f(const Graph<int> &g, const set<int> &prev, const set<int> &cur){
  if(cur.empty()) return 0;

  set<int> next;

  for(auto i : cur){
    for(auto &e : g[i]){
      if(not EXIST(prev, e.to)){
        next.insert(e.to);
      }
    }
  }

  int ret = f(g,cur,next) + 1;

  return ret;
}



int main(){
  int N;
  while(cin >> N){
    Graph<int> g(N);
    vector<string> S(N); cin >> S;
    REP(i,N){
      REP(j,N){
        if(i < j and S[i][j] == '1'){
          add_undirected(g, i, j, 1);
        }
      }
    }

    bool no = not is_bipartite_graph(g);
    


    int ans = 0;

    if(not no){
      REP(i,N){
        set<int> cur;
        for(auto &e : g[i]){
          cur.insert(e.to);
        }
        set<int> temp;
        temp.insert(i);

        chmax(ans, f(g,temp,cur) + 1);
      }
    }


    
    if(no){
      cout << -1 << endl;
    }else{
      cout << ans << endl;
    }
  }
  
  return 0;
}


Measured memory_bytes: 896