#include <bits/stdc++.h>
#include <unistd.h>
 
using namespace std;
 
#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}
 
 
typedef long long ll;
 
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
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; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
//const ll MOD = 1000000007;
const ll MOD = 998244353;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx[4] = { -1,0, 1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
// #define mp make_pair
//#define endl '\n'


#define N 300
vii G(N, vi()); //グラフの隣接リスト表現
vi match(N); //マッチングのペア
vector<bool> used(N); //DFSですでに調べたかのフラグ
int n, m;
vi color(N, -1);

//二部グラフかどうかを判断
bool bipartite() {
	stack<int> st;
	color[0] = 0;
	st.push(0);
	int i, j;
	while (!st.empty()) {
		i = st.top();
		st.pop();
		for (j = 0; j < G[i].size(); j++) {
			if (color[G[i][j]] == color[i]) {
				//cout << "NO" << endl;
				return false;
			}
			else {
				if (color[G[i][j]] == -1) {
					color[G[i][j]] = 1 - color[i];
					st.push(G[i][j]);
				}
			}
		}
	}
	//cout << "YES" << endl;
	return true;
}

int main() {
  int n;
  cin >> n;
  vii s(n, vi(n));
  rep (i, n) {
    rep (j, n) {
      char c;
      cin >> c;
      s[i][j] = c - '0';
      if (s[i][j]) {
        G[i].push_back(j);
      }
    }
  }

  if (not bipartite()) {
    cout << -1 << endl;
    return 0;
  }

  int ans = 0;
  rep (s, n) {
    vi g(n, -2);
    int cnt = 0;
    g[s] = 0;
    queue<pii> qu;
    qu.push(pii(s, cnt));
    bool flag = true;
    int ma = 1;
    while (not qu.empty()) {
      pii temp = qu.front();
      qu.pop();
      int u = temp.first, gr = temp.second;
      rep (i, G[u].size()) {
        int v = G[u][i];
        if (g[v] == -2) {
          g[v] = gr + 1;
          qu.push(pii(v, gr + 1));
          ma = max(ma, gr + 1 + 1);
        }
        else {
          if (g[v] != gr - 1 and g[v] != gr + 1) {
            flag = false;
            break;
          }
        }
      }
      if (not flag) break;
    }
    if (flag) {
      chmax(ans, ma);
    }
  }
  if (ans != 0) {
    cout << ans << endl;
  }
  else {
    cout << -1 << endl;
  }
  
}


Measured memory_bytes: 640