#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) {
  return '"' + s + '"';
}
string to_string(const char* s) {
  return to_string((string) s);
}
string to_string(bool b) {
  return (b ? "true" : "false");
}
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug_out() { cout << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cout << " " << to_string(H);
  debug_out(T...);
}
#ifdef LOCAL
#define debug(...) cout << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
const long long mod = 1e9+7; // CHECK
long long power(long long a, long long b, long long m = mod) {
    if(b < 0) {
        return power(power(a, -b), mod-2);
    }
    long long x = 1;
    while(b) {
        if(b & 1) {
            x = 1ll * x * a % m;
        }
        a = 1ll * a * a % m;
        b /= 2;
    }
    return x;
}
#define ll long long
const int INT_INF = 1e9+9;
const ll LL_INF = 2e18;
const int N = 202;
int a[N][N];
bool bipartite = 1;
string g[N];
int col[N], n;
void dfs(int u, int par) {
    for (int v = 0; v < n; v++) {
        if (g[u][v] == '0') continue;
        if (col[v] != -1 && col[v] == col[u]) {
            bipartite = 0;
            break;
        }
        if (col[v] == -1) {
            col[v] = col[u] ^ 1;
            dfs(v, u);
        }
    }
}
signed main() {  
    ios_base::sync_with_stdio(false); 
    cin.tie(0); cout.tie(0);
    
    cin >> n;
    for (int i = 0; i < n; i++) {
        cin >> g[i];
    }
    memset(col, -1, sizeof col);
    col[0] = 0;
    dfs(0, -1);
    if (bipartite == 0) {
        cout << "-1\n";
        return 0;
    }
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            if(i == j) a[i][j] = 0;
            else {
                a[i][j] = (g[i][j] == '0' ? INT_INF : 1);
            }
        }
    }
    int dia = 0;
    for (int k = 0; k < n; k++) {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                a[i][j] = min(a[i][j], a[i][k] + a[k][j]);
                if (k == n-1) {
                    dia = max(dia, a[i][j]);
                }
            }
        }
    }
    cout << dia + 1 << "\n";

    

    return 0;
}



Measured memory_bytes: 512