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#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx")
#pragma GCC optimize("unroll-loops")    
#include <bits/stdc++.h>
#define pb push_back
#define x first
#define y second
#define mp make_pair
#define len(a) int(a.size())
#define files(FILENAME) read(FILENAME); write(FILENAME)
#define read(FILENAME) freopen((string(FILENAME) + ".in").c_str(), "r", stdin)
#define write(FILENAME) freopen((string(FILENAME) + ".out").c_str(), "w", stdout)
using namespace std;
        
template<typename T1, typename T2>inline void chkmin(T1 &x, T2 y) { if (x > y) x = y; }
template<typename T1, typename T2>inline void chkmax(T1 &x, T2 y) { if (x < y) x = y; } 
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const pair<T, U> &_p) { _out << _p.first << ' ' << _p.second; return _out; }
template<typename T, typename U> inline istream &operator>> (istream &_in, pair<T, U> &_p) { _in >> _p.first >> _p.second; return _in; }
template<typename T> inline ostream &operator<< (ostream &_out, const vector<T> &_v) { if (_v.empty()) { return _out; } _out << _v.front(); for (auto _it = ++_v.begin(); _it != _v.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline istream &operator>> (istream &_in, vector<T> &_v) { for (auto &_i : _v) { _in >> _i; } return _in; }
template<typename T> inline ostream &operator<< (ostream &_out, const set<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const multiset<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const unordered_set<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const unordered_multiset<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const map<T, U> &_m) { if (_m.empty()) { return _out; } _out << '(' << _m.begin()->first << ": " << _m.begin()->second << ')'; for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) { _out << ", (" << _it->first << ": " << _it->second << ')'; } return _out; }
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const unordered_map<T, U> &_m) { if (_m.empty()) { return _out; } _out << '(' << _m.begin()->first << ": " << _m.begin()->second << ')'; for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) { _out << ", (" << _it->first << ": " << _it->second << ')'; } return _out; }
        
typedef long long base; 
typedef pair<int, int> point;      
typedef complex<double> comp;

const int N = 2e3 + 5;

int ans = -1;
int n;
int dist[N];
vector<int> edge[N];

void check(int i) {
    queue<int> que({i});
    fill(dist, dist + n, 1e9);
    dist[i] = 0;
    int mx = 0;
    while (que.size()) {
        auto u = que.front();
        que.pop();
        mx = dist[u];
        for (int v : edge[u]) {
            if (dist[v] > dist[u] + 1) {
                dist[v] = dist[u] + 1;
                que.push(v);
            }
            if (dist[v] == dist[u]) return;
        }
    }
    chkmax(ans, mx + 1);
}

int main() {
    ios::sync_with_stdio(0);
    srand(time(0));
#ifdef ONPC
    freopen("input", "r", stdin);
#endif
    cin >> n;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            char c;
            cin >> c;
            if (c == '1') {
                edge[i].pb(j);
            }
        }
    }
    for (int i = 0; i < n; ++i) check(i);
    cout << ans << '\n';
}  



Measured memory_bytes: 512