#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((lint)(x).size())
#define POW2(n) (1LL << (n))
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const deque<T> &vec){ os << "deq["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa){ os << "(" << pa.first << "," << pa.second << ")"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> bool mmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T> bool mmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; }
template<typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template<typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/tag_and_trait.hpp>
using namespace __gnu_pbds; // find_by_order(), order_of_key()
template<typename TK> using pbds_set = tree<TK, null_type, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename TK, typename TV> using pbds_map = tree<TK, TV, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
*/
struct UndirectedGraph
{
    using pint = pair<int, int>;

    int V, E;

    vector<vector<pint>> to; // to[v1] = [pair(v2, edgeId)]
    vector<pint> edges; // edges[edgeId] = (v1, v2)

    UndirectedGraph(): V(0), E(0) {}
    UndirectedGraph(int V): V(V), E(0)
    {
        to.resize(V);
    }

    void add_edge(int v1, int v2)
    {
        to[v1].push_back(pint(v2, E));
        to[v2].push_back(pint(v1, E));
        edges.push_back(pint(v1, v2));
        E++;
    }

    // v0の連結成分からなる部分グラフが2部グラフかどうか判定
    // 最悪O(N^2)を避けるためbip_color, bip_visitedを一々初期化
    // していない，このため動的にグラフを更新する場合に非対応
    vector<int> bip_color; // 2部グラフ判定彩色 1, 2で塗る
    vector<bool> bip_visited;
    bool is_subgraph_bipartite(int v0)
    {
        bip_color.resize(V);
        bip_visited.resize(V);
        if (!bip_color[v0]) bip_color[v0] = 1;
        queue<int> vs_pending;
        vs_pending.push(v0);
        while (!vs_pending.empty())
        {
            int now = vs_pending.front();
            vs_pending.pop();
            if (bip_visited[now]) continue;

            bip_visited[now] = true;
            for (auto nxt : to[now])
            {
                if (bip_color[nxt.first] == bip_color[now]) return false;
                else if (bip_color[nxt.first] == 0)
                {
                    bip_color[nxt.first] = 3 - bip_color[now];
                    vs_pending.push(nxt.first);
                }
            }
        }

        return true;
    }
};

int N;
vector<string> S(N);
using wedges = vector<vector<plint>>; // (to, weight)

pair<vector<lint>, vector<int>> dijkstra(int N, int s, const wedges &w)
{
    vector<lint> dist(N, 1e9);
    dist[s] = 0;
    vector<int> prev(N, -1);
    priority_queue<plint, vector<plint>, greater<plint>> pq;
    pq.emplace(0, s);
    while (!pq.empty())
    {
        plint p = pq.top();
        pq.pop();
        int v = p.second;
        if (dist[v] < p.first) continue;
        for (auto nx : w[v])
        {
            lint dnx = p.first + nx.second;
            if (dist[nx.first] > dnx)
            {
                dist[nx.first] = dnx, prev[nx.first] = v;
                pq.emplace(dnx, nx.first);
            }
        }
    }
    return make_pair(dist, prev); // (distance, previous_node)
}

int main()
{
    cin >> N;
    S.resize(N);
    cin >> S;

    UndirectedGraph g(N);
    REP(i, N) REP(j, i) if (S[i][j] == '1') g.add_edge(i, j);
    if (!g.is_subgraph_bipartite(0))
    {
        cout << -1 << endl;
        return 0;
    }
    lint ret = 0;
    wedges w(N);
    REP(i, N) REP(j, N) if (S[i][j] == '1')
    {
        w[i].emplace_back(j, 1);
    }
    REP(i, N)
    {
        auto r = dijkstra(N, i, w);
        auto ds = r.first;
        mmax(ret, *max_element(ALL(ds)));
    }
    cout << ret + 1 << endl;
}


Measured memory_bytes: 1024