#if __has_include("../library/Basic/Debug.hpp")

#include "../library/Basic/Debug.hpp"

#else

/* ----- Header Files ----- */
// IO
#include <cstdio>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm
#include <algorithm>
#include <cmath>
#include <numeric>

// container
#include <vector>
#include <array>
#include <string>
#include <tuple>
#include <complex>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <bitset>

// others
#include <random>
#include <limits>
#include <functional>
#include <ctime>
#include <cassert>
#include <cstdint>

/* ----- Type Alias ----- */
using Int = long long int;
using Real = long double;
using std::array;
using std::pair;
using std::string;
using std::tuple;
using std::vector;
template <class T>
using MaxHeap = std::priority_queue<T>;
template <class T>
using MinHeap = std::priority_queue<T, std::vector<T>, std::greater<T>>;

template <class T>
T genv(T v) { return v; }

template <class T, class... Ts>
auto genv(size_t l, Ts... ts) {
    return vector<decltype(genv<T>(ts...))>(l, genv<T>(ts...));
}

template <class Cost = Int>
struct Edge {
    Int src, dst;
    Cost cost;
    Edge(Int src = -1, Int dst = -1, Cost cost = 1)
        : src(src), dst(dst), cost(cost){};

    bool operator<(const Edge<Cost>& e) const { return this->cost < e.cost; }
    bool operator>(const Edge<Cost>& e) const { return this->cost > e.cost; }
};

template <class Cost = Int>
using Edges = vector<Edge<Cost>>;
template <class Cost = Int>
using Graph = vector<vector<Edge<Cost>>>;

#endif

/* ----- Misc ----- */
void fastio() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
}

struct Fout {
    Int precision;
    explicit Fout(Int precision) : precision(precision) {}
};

std::ostream& operator<<(std::ostream& os, const Fout& fio) {
    os << std::fixed << std::setprecision(fio.precision);
    return os;
}

/* ----- Constants ----- */
// constexpr Int INF = std::numeric_limits<Int>::max() / 3;
// constexpr Int MOD = 1000000007;
// const Real PI = acos(-1);
// constexpr Real EPS = 1e-10;
// std::mt19937 mt(int(std::time(nullptr)));

int main() {
    int n;
    std::cin >> n;

    vector<string> s(n);
    for (auto& x : s) {
        std::cin >> x;
    }

    Graph<> graph(n);
    for (int v = 0; v < n; ++v) {
        for (int u = 0; u < v; ++u) {
            if (s[u][v] == '1') {
                graph[v].emplace_back(v, u);
                graph[u].emplace_back(u, v);
            }
        }
    }

    int ans = -1;
    for (int r = 0; r < n; ++r) {
        bool ok = true;
        vector<std::set<int>> vs(1);
        vs[0].insert(r);

        std::queue<int> que;
        que.push(r);

        while (!que.empty()) {
            int v = que.front();
            que.pop();

            int f;
            for (f = 0; f < vs.size(); ++f) {
                if (vs[f].count(v)) break;
            }
            assert(f < vs.size());

            for (auto e : graph[v]) {
                int u = e.dst;
                int g;
                for (g = 0; g < vs.size(); ++g) {
                    if (vs[g].count(u)) break;
                }

                if (g == vs.size()) {
                    if (f + 1 == vs.size()) {
                        vs.push_back(std::set<int>());
                    }
                    vs[f + 1].insert(u);
                    que.push(u);
                } else {
                    if (std::abs(f - g) != 1) {
                        ok = false;
                        break;
                    }
                }
            }
        }

        if (ok) {
            ans = std::max(ans, (int)vs.size());
        }
    }

    std::cout << ans << std::endl;
    return 0;
}


Measured memory_bytes: 1536