//#define NDEBUG
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <iterator>
#include <vector>

namespace n91 {

  using i8 = std::int_fast8_t;
  using i32 = std::int_fast32_t;
  using i64 = std::int_fast64_t;
  using u8 = std::uint_fast8_t;
  using u32 = std::uint_fast32_t;
  using u64 = std::uint_fast64_t;
  using isize = std::ptrdiff_t;
  using usize = std::size_t;

  constexpr usize operator"" _z(unsigned long long x) noexcept {
    return static_cast<usize>(x);
  }

  template <class T> class integral_iterator {
  public:
    using difference_type = T;
    using value_type = T;
    using pointer = const value_type*;
    using reference = value_type;
    using iterator_category = std::random_access_iterator_tag;

  private:
    using self_type = integral_iterator<value_type>;
    value_type i;

  public:
    constexpr integral_iterator() noexcept : i() {}
    explicit constexpr integral_iterator(const value_type i) noexcept : i(i) {}
    constexpr self_type operator++(int) noexcept { return self_type(i++); }
    constexpr self_type operator--(int) noexcept { return self_type(i--); }
    constexpr self_type operator[](const difference_type rhs) const noexcept {
      return self_type(i + rhs);
    }
    constexpr self_type& operator++() noexcept {
      ++i;
      return *this;
    }
    constexpr self_type& operator--() noexcept {
      --i;
      return *this;
    }
    constexpr reference operator*() const noexcept { return i; }
    constexpr self_type operator+(const difference_type rhs) const noexcept {
      return self_type(i + rhs);
    }
    constexpr self_type operator-(const difference_type rhs) const noexcept {
      return self_type(i - rhs);
    }
    constexpr difference_type operator-(const self_type rhs) const noexcept {
      return i - rhs.i;
    }
    constexpr bool operator<(const self_type rhs) const noexcept {
      return i < rhs.i;
    }
    constexpr bool operator<=(const self_type rhs) const noexcept {
      return i <= rhs.i;
    }
    constexpr bool operator>(const self_type rhs) const noexcept {
      return i > rhs.i;
    }
    constexpr bool operator>=(const self_type rhs) const noexcept {
      return i >= rhs.i;
    }
    constexpr bool operator==(const self_type rhs) const noexcept {
      return i == rhs.i;
    }
    constexpr bool operator!=(const self_type rhs) const noexcept {
      return i != rhs.i;
    }
    constexpr self_type& operator+=(const difference_type rhs) noexcept {
      i += rhs;
      return *this;
    }
    constexpr self_type& operator-=(const difference_type rhs) noexcept {
      i -= rhs;
      return *this;
    }
  };
  template <class T>
  constexpr integral_iterator<T> make_int_itr(const T i) noexcept {
    return integral_iterator<T>(i);
  }
  class rep {
    const usize f, l;

  public:
    constexpr rep(const usize f, const usize l) noexcept : f(f), l(l) {}
    constexpr auto begin() const noexcept { return make_int_itr(f); }
    constexpr auto end() const noexcept { return make_int_itr(l); }
  };
  class revrep {
    const usize f, l;

  public:
    revrep(const usize f, const usize l) noexcept : f(l), l(f) {}
    auto begin() const noexcept {
      return std::make_reverse_iterator(make_int_itr(f));
    }
    auto end() const noexcept {
      return std::make_reverse_iterator(make_int_itr(l));
    }
  };
  template <class T> auto md_vec(const usize n, const T& value) {
    return std::vector<T>(n, value);
  }
  template <class... Args> auto md_vec(const usize n, Args... args) {
    return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
  }
  template <class T> constexpr T difference(const T& a, const T& b) {
    return a < b ? b - a : a - b;
  }
  template <class T> T scan() {
    T ret;
    std::cin >> ret;
    return ret;
  }

} // namespace n91

#include <algorithm>
#include <iostream>
#include <utility>

namespace n91 {

  void main_() {
    const usize n = scan<usize>();
    std::vector<std::string> s(n);
    for (auto& e : s) {
      std::cin >> e;
    }

    const auto solve = [&](const usize st) -> int {
      std::vector<bool> used(n, false);
      used[st] = true;
      usize cnt = 1_z;
      int ret = 1;
      std::vector<usize> cur, nex;
      cur.push_back(st);
      while (cnt != n) {
        for (const auto v : cur) {
          for (const auto i : rep(0_z, n)) {
            if (s[v][i] == '1' && !used[i]) {
              ++cnt;
              used[i] = true;
              nex.push_back(i);
            }
          }
        }
        for (const auto u : nex) {
          for (const auto v : nex) {
            if (s[u][v] == '1') {
              return -1;
            }
          }
        }
        cur = std::move(nex);
        nex.clear();
        ++ret;
      }
      return ret;
    };

    int ans = -1;
    for (const auto i : rep(0_z, n)) {
      ans = std::max(ans, solve(i));
    }
    std::cout << ans << std::endl;
  }

} // namespace n91

int main() {
  n91::main_();
  return 0;
}


Measured memory_bytes: 256