#include <algorithm>
#include <functional>
#include <iostream>
#include <iomanip>
#include <vector>
#include <map>
#include <set>
#include <unordered_set>
#include <queue>
#include <numeric>
#include <bitset>
#include <cmath>

using namespace std;
using ll = long long;
using ull = unsigned long long;
// const ll mod =  998244353 ;
const ll mod = 1000000007;
const ll inf = 1e18;
const int intinf = 1e9;
const int dx[] = {1, -1, 0, 0};
const int dy[] = {0, 0, 1, -1};


#define REP(i, n) for (ll i = 0; i < (n); ++i)
#define REP_FROM(i, j, n) for (ll i = (j); i < (n); ++i)
#define REP_REV(i, n) for (ll i = n-1; i >= 0; --i)
#define all(x) (x).begin(),(x).end()
#define sz(x) ll(x.size())

template<typename T>
void print_vec(vector<T> a) {
  int n = a.size();
  REP(i, n) {
    cout >> a[i];
    if (i != n - 1) cout << " "; else cout << endl;
  }
}

ll power(ll base, ll exponent) {
  if (exponent % 2) {
    return power(base, exponent - 1) * base % mod;
  }
  else if (exponent) {
    ll root_ans = power(base, exponent / 2);
    return root_ans * root_ans % mod;
  }
  else { return 1; }
}

ll inverse(ll x) { return power(x, mod - 2); }

ll gcd(ll a, ll b) {
  if (a < b) gcd(b, a);
  ll r;
  while (r = a % b) {
    a = b;
    b = r;
  }
  return b;
}

template<typename T>
ll sum(T begin, T end) { return accumulate(begin, end, 0ll); }

struct combination {
    vector<ll> fact, inv;

    combination(int sz) : fact(sz + 1), inv(sz + 1) {
      fact[0] = 1;
      for (int i = 1; i <= sz; i++) { fact[i] = fact[i - 1] * i % mod; }
      inv[sz] = power(fact[sz], mod - 2);
      for (int i = sz - 1; i >= 0; i--) { inv[i] = inv[i + 1] * (i + 1) % mod; }
    }

    ll C(int p, int q) const {
      if (q < 0 || p < q) return 0;
      return (fact[p] * inv[q] % mod * inv[p - q] % mod);
    }
};

using Pair = pair<ll, ll>;

template<ll Modulus>
struct ModInt {
    ll a;

    constexpr ModInt(const ll x = 0) noexcept  : a((x % mod + mod) % mod) {}

    constexpr ll &value() noexcept { return a; }

    constexpr const ll &value() const noexcept { return a; }

    constexpr ModInt operator+(const ModInt x) const noexcept {
      return ModInt(*this) += x;
    }

    constexpr ModInt operator-(const ModInt x) const noexcept {
      return ModInt(*this) -= x;
    }

    constexpr ModInt operator*(const ModInt x) const noexcept {
      return ModInt(*this) *= x;
    }

    constexpr ModInt operator/(const ModInt x) const noexcept {
      return ModInt(*this) /= x;
    }

    constexpr ModInt &operator+=(const ModInt x) noexcept {
      a += x.a;
      if (a >= Modulus) {
        a -= Modulus;
      }
      return *this;
    }

    constexpr ModInt &operator-=(const ModInt x) noexcept {
      if (a < x.a) {
        a += Modulus;
      }
      a -= x.a;
      return *this;
    }

    constexpr ModInt &operator*=(const ModInt x) noexcept {
      a = a * x.a % Modulus;
      return *this;
    }

    constexpr ModInt &operator/=(ModInt x) noexcept {
      ll exp = Modulus - 2;
      while (exp) {
        if (exp % 2) {
          *this *= x;
        }
        x *= x;
        exp /= 2;
      }
      return *this;
    }

    constexpr ModInt operator-() noexcept {
      return ModInt(-a);
    }

    friend ostream &operator<<(ostream &os, const ModInt &m) {
      os << m.a;
      return os;
    }
};

using mint = ModInt<mod>;


bool check(const vector<vector<int>>& m, vector<int> & color, int i, int c) {
  if(color[i] == c) return true;
  if(color[i] != -1) return false;
  color[i] = c;
  for(int x :m[i]) {
    bool tmp = check(m, color, x, (c + 1) % 2);
    if(!tmp) return false;
  }
  return true;
}

signed main() {
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(15);
  ll n;
  cin >> n;
  vector<vector<int>> a(n), m(n, vector<int>(n, intinf));
  REP(i, n) {
    string s;
    cin >> s;
    REP(j, n) {
      if (s[j] == '1') {
        a[i].push_back(j);
        m[i][j] = 1;
      }
    }
  }
  vector<int> color(n, -1);
  if(!check(a, color, 0, 0)) {
    cout << -1 << endl;
    return 0;
  }
  REP(k, n) {
    REP(i, n) {
      REP(j, n) {
        m[i][j] = min(m[i][j], m[i][k] + m[k][j]);
      }
    }
  }
  int ans = 0;
  REP(i, n) {
    REP_FROM(j, i+1, n) {
      ans = max(ans, m[i][j] + 1);
    }
  }
  cout << ans << endl;
  return 0;
}


Measured memory_bytes: 640