#include <bits/stdc++.h>
#define range(i, l, r) for(long long int (i) = (l); (i) < (r); (i)++)
#define reversed_range(i, l, r) for (long long int (i) = (r) - 1; (i) >= l; (i)--)
using namespace std;
template <typename T>
using vec = vector<T>;
using lint = long long;
using ulint = unsigned long long;
using pint = pair<int, int>;
using plint = pair<lint, lint>;

template <typename S, typename T>
ostream& operator <<(ostream& os, pair<S, T> p) {
    os << "(";
    os << p.first << ", " << p.second;
    return os << ")";
}

template <typename T>
ostream& operator <<(ostream& os, vec<T> v) {
    os << "[";
    if (v.size() == 0) return os << "]";
    for (int i = 0; i < v.size() - 1; i++) {
        os << v.at(i) << ", ";
    }
    return os << v.at(v.size() - 1) << "]";
}

template <typename T>
ostream& operator <<(ostream& os, set<T>& s) {
    os << "{";
    if (s.begin() == s.end()) return os << "}";
    auto it_first_item = s.begin();
    cout << *it_first_item;
    for (auto it = ++it_first_item; it != s.end(); it++) {
        cout << ", " << *it;
    }
    return cout << "}";
}

template <typename T>
ostream& operator <<(ostream& os, unordered_set<T>& s) {
    os << "{";
    if (s.begin() == s.end()) return os << "}";
    auto it_first_item = s.begin();
    cout << *it_first_item;
    for (auto it = ++it_first_item; it != s.end(); it++) {
        cout << ", " << *it;
    }
    return cout << "}";
}

template <typename K, typename V>
ostream& operator <<(ostream& os, map<K, V> m) {
    os << "{";
    if (m.begin() == m.end()) return os << "}";
    auto it_first_item = m.begin();
    cout << it_first_item->first << ": " << it_first_item->second;
    for (auto it = ++it_first_item; it != m.end(); it++) {
        cout << ", " << it->first << ": " << it->second;
    }
    return os << "}";
}

template <typename K, typename V>
ostream& operator <<(ostream& os, unordered_map<K, V> m) {
    os << "{";
    if (m.begin() == m.end()) return os << "}";
    auto it_first_item = m.begin();
    cout << it_first_item->first << ": " << it_first_item->second;
    for (auto it = ++it_first_item; it != m.end(); it++) {
        cout << ", " << it->first << ": " << it->second;
    }
    return os << "}";
}

lint pow(lint num, lint e, lint MOD) {
    lint res = 1;
    lint cur_num = num;
    while (e) {
        if (e & 1) {
            res *= cur_num;
            res %= MOD;
        }
        cur_num *= cur_num;
        cur_num %= MOD;
        e >>= 1;
    }
    return res;
}

int main() {
    cin.tie(0); cout.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    lint N; cin >> N;
    vec<vec<bool>> is_connected(N, vec<bool>(N));
    range(i, 0, N) {
        string row; cin >> row;
        range(j, 0, N) is_connected.at(i).at(j) = (row.at(j) == '1');
    }
    vec<lint> color(N, -1);
    const lint BLACK = 0, WHITE = 1;
    color.at(0) = WHITE;
    function<bool(lint)> draw_color = [&](lint node) {
        lint next_color = color.at(node) ^ 1;
        range(neighbor, 0, N) {
            if (!is_connected.at(node).at(neighbor)) continue;
            else if (color.at(neighbor) == -1) {
                color.at(neighbor) = next_color;
                if (!draw_color(neighbor)) return false;
            }
            else if (color.at(neighbor) != next_color) return false;
        }
        return true;
    };
    if (!draw_color(0)) {
        cout << -1 << "\n";
        return 0;
    }
    vec<vec<lint>> min_dist(N, vec<lint>(N, 1LL << 58));
    range(i, 0, N) min_dist.at(i).at(i) = 0;
    range(i, 0, N) range(j, 0, N) {
        if (is_connected.at(i).at(j)) min_dist.at(i).at(j) = 1;
    }
    range(k, 0, N) range(i, 0, N) range(j, 0, N) {
        min_dist.at(i).at(j) = min(min_dist.at(i).at(j),
            min_dist.at(i).at(k) + min_dist.at(k).at(j));
    }
    lint max_dist = 0;
    range(i, 0, N) range(j, 0, N) max_dist = max(max_dist, min_dist.at(i).at(j));
    cout << max_dist + 1 << "\n";
}

Measured memory_bytes: 640