#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <queue>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cmath>
#include <numeric>
#include <iomanip>
#include <stack>
#include <complex>
#include <functional>
#include <tuple>

using namespace std;

#define Rep(i,a,b) for(ll i = a; i < b; ++i)
#define rep(i,b) Rep(i,0,b)
#define allof(a) (a).begin(), (a).end()

#define Yes(q) ((q) ? "Yes" : "No")
#define YES(q) ((q) ? "YES" : "NO")
#define Possible(q) ((q) ? "Possible" : "Impossible")
#define POSSIBLE(q) ((q) ? "POSSIBLE" : "IMPOSSIBLE")

using ll = long long;

constexpr int inf = 1e9 + 7;
constexpr ll infll = 1ll << 60ll;
constexpr ll mod = 998244353;
// 0~3までは右下左上 4~7までは斜め
constexpr int dx[] = { 1, 0, -1, 0, 1, 1, -1, -1 };
constexpr int dy[] = { 0, 1, 0, -1, -1, 1, 1, -1 };

namespace {
    template<typename T> bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
    template<typename T> bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }

    void Cout(long long x, const char* end = "\n") { std::cout << x << end; }
    template <typename T> void Cout(const T& x, const char* end = "\n") { std::cout << x << end; }
    template <typename T> void Cout(const std::vector<T>& x, const char* sep = " ", const char* end = "\n") { for (std::size_t i = 0, sz = x.size(); i < sz; ++i) { std::cout << x[i] << (i == sz - 1 ? end : sep); } }

    // 標準入出力
    struct inp {
        std::size_t szi, szj;
        inp(std::size_t _szi = 1, std::size_t _szj = 1) : szi(_szi), szj(_szj) {}
        template <typename T> operator T () const { T a; std::cin >> a; return a; }
        template <typename T> operator std::vector<T>() const { std::vector<T> a(szi); for (std::size_t i = 0; i < szi; ++i) std::cin >> a[i]; return a; }
        template <typename T> operator std::vector<std::vector<T>>() const {
            std::vector<std::vector<T>> a(szi, std::vector<T>(szj));
            for (std::size_t i = 0; i < szi; ++i) for (std::size_t j = 0; j < szj; ++j) cin >> a[i][j]; return a;
        }
    };
    inp inp1;

    struct Edge {
        ll from; // 移動前のノード
        ll to; // 移動先のノード
        ll cost; // 辺のコスト
        ll hoge; // 任意変更 いらないかも

        Edge() = default;
        Edge(ll _to) : from(-1), to(_to), cost(1), hoge(-1) {};
        Edge(ll _to, ll _cost) : from(-1), to(_to), cost(_cost), hoge(-1) {};
        Edge(ll _from, ll _to, ll _cost) : from(_from), to(_to), cost(_cost), hoge(-1) {};
        Edge(ll _from, ll _to, ll _cost, ll _hoge) : from(_from), to(_to), cost(_cost), hoge(_hoge) {};
        bool operator< (const Edge& rhs) const {
            return cost < rhs.cost;
        }
        bool operator> (const Edge& rhs) const {
            return cost > rhs.cost;
        }
    };

    using Graph = vector<vector<Edge>>;
}

int main() {

    int n = inp1;
    vector<string> s = inp(n);
    Graph G(n);

    rep(i, n) {
        rep(j, s[i].size()) {
            if (s[i][j] == '1') G[i].emplace_back(Edge(j));
        }
    }

    int ans = -1;

    rep(i, n) {
        bool can = true;

        vector<bool> used(n, false);
        used[i] = true;

        queue<int> que;
        que.emplace(i);

        int cnt = 0;

        vector<int> rank(n, -100);

        while (!que.empty()) {
            ++cnt;
            set<int> set;
            while (!que.empty()) {
                int u = que.front();
                que.pop();
                rank[u] = cnt;
                for (const auto& edge : G[u]) {
                    // 前回のならおｋ
                    if (rank[edge.to] != cnt - 1 && used[edge.to]) {
                        can = false;
                        break;
                    }
                    if (used[edge.to]) continue;
                    set.emplace(edge.to);
                }
            }

            if (!can) break;

            for (auto v : set) {
                que.emplace(v);
                used[v] = true;
            }
        }

        if (can) chmax(ans, cnt);
    }

    Cout(ans);

    return 0;
}


Measured memory_bytes: 1920