#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template <class T> using treap = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define int long long
#define REP(i, n) for (long long i = 0, max_i = (n); i < max_i; i++)
#define REPI(i, a, b) for (long long i = (a), max_i = (b); i < max_i; i++)
#define ALL(obj) begin(obj), end(obj)
#define RALL(obj) rbegin(obj), rend(obj)
#define fi first
#define se second
using ii = pair<int, int>;
vector<ii> dirs = {
    {1, 0}, {0, 1}, {-1, 0}, {0, -1},  // 4方向
    {1, 1}, {-1, 1}, {-1, -1}, {1, -1},  // 斜め
    {0, 0},  // 自身
};
template <class T> inline bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } return false; }
template <class T> inline bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; } return false; }
template <class T, class S> vector<T> make_vec(size_t n, S x) { return vector<T>(n, x); }
template <class T, class... Ts> auto make_vec(size_t n, Ts... ts) { return vector<decltype(make_vec<T>(ts...))>(n, make_vec<T>(ts...)); }

// debug
template <class T> ostream& operator<<(ostream& s, vector<T>& d) { REP (i, d.size()) s << d[i] << (i == d.size() - 1 ? "" : " "); return s; }
template <class T> ostream& operator<<(ostream& s, vector<vector<T>>& d) { REP (i, d.size()) s << d[i] << (i == d.size() - 1 ? "" : "\n"); return s; }
template <class T, class S> ostream& operator<<(ostream& s, pair<T, S>& p) { s << "{" << p.first << ", " << p.second << "}"; return s; }
template <class T> ostream& operator<<(ostream& s, set<T> m) { for (auto it = m.begin(); it != m.end(); it++) { s << *it << (next(it) == m.end() ? "" : "\n"); } return s; }
template <class T> ostream& operator<<(ostream& s, multiset<T> m) { for (auto it = m.begin(); it != m.end(); it++) { s << *it << (next(it) == m.end() ? "" : "\n"); } return s; }
template <class T, class S> ostream& operator<<(ostream& s, map<T, S> m) { for (auto it = m.begin(); it != m.end(); it++) { s << *it << (next(it) == m.end() ? "" : "\n"); } return s; }
template <class T, class S> ostream& operator<<(ostream& s, unordered_map<T, S> m) { for (auto it = m.begin(); it != m.end(); it++) { s << *it << (next(it) == m.end() ? "" : "\n"); } return s; }
#ifdef _MY_DEBUG
    #define dump(...) cerr << "/* " << #__VA_ARGS__ << " :[" << __LINE__ << ":" << __FUNCTION__ << "]" << endl, dump_func(__VA_ARGS__), cerr << "*/\n\n";
#else
    #define dump(...)
    #define endl "\n"
#endif
void dump_func() { cerr << endl; }
template <class Head, class... Tail> void dump_func(Head&& h, Tail&&... t) { cerr << h << (sizeof...(Tail) == 0 ? "" : ", "), dump_func(forward<Tail>(t)...); }

struct Fast { Fast() { cin.tie(nullptr); ios::sync_with_stdio(false); } } fast;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
constexpr int MOD = 1000000007;
// *************** TEMPLATE END *************** 

signed main() {
    int n; cin >> n;
    auto d = make_vec<int>(n, n, 0);
    REP (i, n) {
        REP (j, n) {
            char c; cin >> c;
            d[i][j] = c == '1';
        }
    }
    vector<int> color(n);
    function<bool(int, int)> dfs = [&](int v, int c) {
        color[v] = c;
        REP (i, n) if (d[v][i]) {
            if (color[i] == c) return false;
            if (color[i] == 0) {
                if (!dfs(i, -c)) return false;
            }
        }
        return true;
    };
    if (!dfs(0, 1)) {
        cout << -1 << endl;
        return 0;
    }
    int ma = 1;
    REP (i, n) {
        vector<int> idx(n, -1);
        idx[i] = 0;
        queue<int> q;
        q.push(i);
        while (!q.empty()) {
            int v = q.front(); q.pop();
            REP (j, n) if (d[v][j] && idx[j] == -1) {
                idx[j] = idx[v] + 1;
                q.push(j);
            }
        }
        REP (j, n) chmax(ma, idx[j] + 1);
    }
    cout << ma << endl;
    // if (mi != INF) {
    //     cout << mi << endl;
    //     return 0;
    // }

    // // 木
    // int diameter = 0;
    // function<int(int, int)> dfs2 = [&](int v, int p) {
    //     int ma = 0;
    //     REP (s, n) if (d[v][s]) {
    //         if (s != p) {
    //             int tmp = dfs2(s, v) + 1;
    //             diameter = max(diameter, ma + tmp);
    //             ma = max(ma, tmp);
    //         }
    //     }
    //     return ma;
    // };
    // dfs2(0, -1);
    // cout << diameter + 1 << endl;
}


Measured memory_bytes: 640