#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>
using namespace std;
#ifdef LOCAL_DEV
	#define debug(var) std::cout<<#var" = "<<var<<std::endl
#else
	#define debug(var)
#endif
#ifdef LOCAL_TEST
	#define BOOST_STACKTRACE_USE_ADDR2LINE
	#define BOOST_STACKTRACE_ADDR2LINE_LOCATION /usr/local/bin/addr2line
	#define _GNU_SOURCE
	#include <boost/stacktrace.hpp>
	template<typename T> class dvector : public std::vector<T> {
	public:
		dvector() : std::vector<T>() {}
		explicit dvector(size_t n, const T& value = T()) : std::vector<T>(n,value) {}
		dvector(const std::vector<T>& v) : std::vector<T>(v) {}
		dvector(const std::initializer_list<T> il) : std::vector<T>(il) {}
		dvector(const typename std::vector<T>::iterator first, const typename std::vector<T>::iterator last) : std::vector<T>(first, last) {}
		dvector(const std::string::iterator first, const std::string::iterator last) : std::vector<T>(first, last) {}
		T& operator[](size_t n) {
			try { return this->at(n); } catch (const std::exception& e) {
				std::cerr << boost::stacktrace::stacktrace() << endl; return this->at(n);
			}
		}
		const T& operator[](size_t n) const {
			try { return this->at(n); } catch (const std::exception& e) {
				std::cerr << boost::stacktrace::stacktrace() << endl; return this->at(n);
			}
		}
	};
	class dbool{
	public:
		dbool() : boolvalue(false) {}
		dbool(bool b) : boolvalue(b) {}
		dbool(const dbool &b) : boolvalue(b.boolvalue) {}
		operator bool&() { return boolvalue; }
		operator const bool&() const { return boolvalue; }
	private:
		bool boolvalue;
	};
	template<typename T1, typename T2> ostream& operator<<(ostream& s, pair<T1, T2>& p) {return s << "(" << p.first << ", " << p.second << ")";}
	template<typename T> ostream& operator<<(ostream& s, dvector<T>& v) {
		for (int i = 0, len = v.size(); i < len; ++i){ s << v[i]; if (i < len - 1) s << "\t"; } return s; }
	template<typename T> ostream& operator<<(ostream& s, dvector< dvector<T> >& vv) {
		for (int i = 0, len = vv.size(); i < len; ++i){ s << vv[i] << endl; } return s; }
	template<typename T1, typename T2> ostream& operator<<(ostream& s, map<T1, T2>& m) {
		s << "{" << endl; for (auto itr = m.begin(); itr != m.end(); ++itr){ s << "\t" << (*itr).first << " : " << (*itr).second << endl; } s << "}" << endl; return s; }
	template<typename T> ostream& operator<<(ostream& s, set<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}" << endl; return s; }
	template<typename T> ostream& operator<<(ostream& s, multiset<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}" << endl; return s; }
	#define vector dvector
	#define bool dbool
#endif
//#define int long long
using bll = boost::multiprecision::cpp_int;
using ll = long long;
//constexpr int INF = 1e9;//INT_MAX=(1<<31)-1=2147483647
constexpr ll INF = (ll)1e18;//(1LL<<63)-1=9223372036854775807
constexpr ll MOD = (ll)1e9 + 7;
constexpr double EPS = 1e-9;
constexpr int dx[4]={1,0,-1,0};
constexpr int dy[4]={0,1,0,-1};
#define p(var) std::cout<<var<<std::endl
#define PI (acos(-1))
#define rep(i, n)   for(ll i=0, i##_length=(n); i< i##_length; ++i)
#define repeq(i, n) for(ll i=1, i##_length=(n); i<=i##_length; ++i)
#define all(v) (v).begin(), (v).end()
#define uniq(v) (v).erase(unique((v).begin(), (v).end()), (v).end());
template<typename T> inline void pv(vector<T> v) { for(ll i=0, N=v.size(); i<N; i++) cout<< v[i] << (i==N-1 ? '\n' : ' '); }
template<typename T> inline T gcd(T a, T b) { return b ? gcd(b,a%b) : a; }
template<typename T> inline T lcm(T a, T b) { return a / gcd(a,  b) * b; }
template<typename T1, typename T2> inline T1 power(T1 x, T2 n){ return n ? power(x*x%MOD,n/2)*(n%2?x:1)%MOD : 1; }
template<typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template<typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

/*-----8<-----8<-----*/

void warshall_floyd(vector<vector<ll>> &d) {
	ll N=d.size();
	for (ll k=0; k<N; k++) {
		for (ll i=0; i<N; i++) {
			for (ll j=0; j<N; j++){
				if(d[i][k] != INF && d[k][j] != INF && d[i][k] + d[k][j] < d[i][j]){
					d[i][j] = d[i][k] + d[k][j];
				}
			}
		}
	}
}

bool dfs(vector<vector<ll>> &g,ll v,ll p,vector<ll> &seen){
	for(ll nextv:g[v]){
		if(seen[nextv]!=0){
			if(seen[nextv]==seen[v])return false;
			else continue;
		}
		seen[nextv]=-1*seen[v];
		bool b=dfs(g,nextv,v,seen);
		if(!b)return false;
	}
	return true;
}

signed main() {
	ll N;
	cin>>N;
	vector<vector<ll>> g(N);
	vector<vector<ll>> d(N, vector<ll>(N, 0));
	for(ll i=0; i<N; i++) {
		for(ll j=0; j<N; j++) {
			if(i==j) d[i][j] = 0;
			else d[i][j] = INF;
		}
	}

	rep(i,N){
		string s;
		cin>>s;
		rep(j,s.size()){
			if(s[j]=='1'){
				g[i].push_back(j);
				d[i][j]=1;
			}
		}
	}

	vector<ll> seen(N,0);
	seen[0]=1;
	bool b=dfs(g,0,-1,seen);
	if(!b){
		p(-1);return 0;
	}

	ll maxval=0;
	warshall_floyd(d);
	for(ll i=0; i<N; i++) {
		for(ll j=0; j<N; j++) {
			chmax(maxval,d[i][j]);
		}
	}	
	p(1+maxval);
	return 0;
}


Measured memory_bytes: 1024