#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <string>
#include <math.h>
#include <iomanip>
#include <limits>
#include <list>
#include <queue>
#include <tuple>
#include <map>
#include <stack>
#include <set>
using namespace std;
#define MOD (long long int)(1e9+7)
#define ll long long int
#define rep(i,n) for(int i=0; i<(int)(n); i++)
#define reps(i,n) for(int i=1; i<=(int)(n); i++)
#define REP(i,n) for(int i=n-1; i>=0; i--)
#define REPS(i,n) for(int i=n; i>0; i--)
#define INF (int)(1123456789)
#define LINF (long long int)(112345678901234567)
#define chmax(a, b) a = (((a)<(b)) ? (b) : (a))
#define chmin(a, b) a = (((a)>(b)) ? (b) : (a))
#define all(v) v.begin(), v.end()

const int N = (int)3e5;

ll mpow(ll a, ll b){
  if(b==0) return 1;
  else if(b%2==0){ll memo = mpow(a,b/2); return memo*memo%MOD;}
  else return mpow(a,b-1) * a % MOD;
}
ll lpow(ll a, ll b){
  if(b==0) return 1;
  else if(b%2==0){ll memo = lpow(a,b/2); return memo*memo;}
  else return lpow(a,b-1) * a;
}
ll gcd(ll a, ll b){
  if(b==0) return a;
  else return gcd(b, a%b);
}
vector<ll> kaijo_memo;
ll kaijo(ll n){
  if(kaijo_memo.size() > n) return kaijo_memo[n];
  if(kaijo_memo.size() == 0) kaijo_memo.push_back(1);
  while(kaijo_memo.size() <= n) kaijo_memo.push_back(kaijo_memo[kaijo_memo.size()-1] * kaijo_memo.size() % MOD);
  return kaijo_memo[n];
}
vector<ll> gyaku_kaijo_memo;
ll gyaku_kaijo(ll n){
  if(gyaku_kaijo_memo.size() > n) return gyaku_kaijo_memo[n];
  if(gyaku_kaijo_memo.size() == 0) gyaku_kaijo_memo.push_back(1);
  while(gyaku_kaijo_memo.size() <= n) gyaku_kaijo_memo.push_back(gyaku_kaijo_memo[gyaku_kaijo_memo.size()-1] * mpow(gyaku_kaijo_memo.size(), MOD-2) % MOD);
  return gyaku_kaijo_memo[n];
}

ll nCr(ll n, ll r){
  if(n == r) return 1;//0個の丸と-1個の棒みたいな時に時に効く？不安.
  if(n < r || r < 0) return 0;
  ll ret = 1;
  ret *= kaijo(n); ret %= MOD;
  ret *= gyaku_kaijo(r); ret %= MOD;
  ret *= gyaku_kaijo(n-r); ret %= MOD;
  return ret;
}

vector<int> G[N];

int main(void){
  int n;
  cin>>n;
  vector<string> S;
  rep(i,n){
    string s;
    cin>>s;
    S.push_back(s);
  }
  rep(i,n){
    rep(j,n){
      if(i <= j) continue;
      if(S[i][j] == '1'){
        G[i].push_back(j);
        G[j].push_back(i);
      }
    }
  }

  queue<int> q;
  int guki[N];
  bool checked[N];
  rep(i,n){
    guki[i] = -1;
    checked[i] = false;
  }
  q.push(0);
  guki[0] = 0;
  while(q.size() > 0){
    int now = q.front(); q.pop();
    if(checked[now]) continue;
    checked[now] = true;
    rep(i, G[now].size()){
      int next = G[now][i];
      if(guki[next] == -1){
        guki[next] = (1-guki[now]);
        q.push(next);
      }else{
        if(guki[next] == guki[now]){
          cout<<-1<<endl;
          return 0;
        }
      }
    }
  }

  ll ans = 0;
  rep(root, n){
    rep(i,n){
      checked[i] = false;
    }
    while(q.size() > 0) q.pop();
    q.push(root);
    ll count = 0;
    while(q.size() > 0){
      queue<int> q2;
      count++;
      while(q.size() > 0){
        int now = q.front(); q.pop();
        if(checked[now]) continue;
        checked[now] = true;
        rep(i,G[now].size()){
          int next = G[now][i];
          if(checked[next]) continue;
          q2.push(next);
        }
      }
      q = q2;
    }
    chmax(ans, count);
  }
  cout<<ans<<endl;
  return 0;
}


Measured memory_bytes: 7552