#include<iostream>
#include<bits/stdc++.h>

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define rep_r(i, n) for(int i = n-1; i >= 0; i--)
#define rep1(i, n) for(int i = 1; i <= (int)(n); i++)
#define REP(i,n) for(int i=0, i##_len=(n); i<i##_len; ++i)
#define all(x) (x).begin(),(x).end()
#define SZ(x) ((ll)(x).size())
#define bit(n) (1LL<<(n))
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );

#define INF bit(60)
#define pb push_back
#define mod 1000000007

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

using namespace std;
using uif=uint_fast64_t;
using ll=long long int;
using tTree=__gnu_pbds::tree< ll , __gnu_pbds::null_type, less< ll >, __gnu_pbds::rb_tree_tag, __gnu_pbds::tree_order_statistics_node_update>;

int qp(int a,ll b){int ans=1;do{if(b&1)ans=1ll*ans*a%mod;a=1ll*a*a%mod;}while(b>>=1);return ans;}
int qp(int a,ll b,int mo){int ans=1;do{if(b&1)ans=1ll*ans*a%mo;a=1ll*a*a%mo;}while(b>>=1);return ans;}

int gcd(int a,int b){return b?gcd(b,a%b):a;}
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};


#define FACSIZE 2002

ll invfac[FACSIZE];
ll fac[FACSIZE];

ll mod_pow(ll ,ll );
ll mod_add(ll ,ll );
ll mod_mul(ll ,ll );
ll mod_div(ll ,ll );
void make_fact(ll );
void make_invfact(ll );

ll enc(ll a,ll b){
  ll m=min(a,b);
  ll M=max(a,b);
  return m*1000+M;

}

int main(void){

  ll n;
  cin>>n;
  //vector<vector<char>> arr(n,vector<char>(n));

  vector<vector<ll>> graph(n,vector<ll>());

  rep(i,n){
    rep(j,n){
      char c;
      cin>>c;
      ////arr[i][j]=(ll)(c - '0' );
      //arr[i][j]=c;
      if(c=='1') graph[i].push_back(j);
    }
  }



  ll ans=0;
  /*
  for( ll i=0;i<n;i++ ){
    auto v=graph[i];
    cout << "v:" << i << endl;
    for(auto x:v) cout << x << " ";
    cout << endl;
  }
  */

  for(ll i=0;i<n;i++){
    //cout << "i:"<< i << endl;
    unordered_set<ll> unse_edge;
    vector<ll> node(n,-1);
    node.resize(n,-1);
    unse_edge.clear();
    queue<ll> que;
    que.push(i);
    node[i]=0;
    while(!que.empty()){
      auto q=que.front();
      //cout << "q:" << q << endl;
      que.pop();
      for( auto e:graph[q] ){
        if( unse_edge.find( enc(q,e) ) == end(unse_edge) ){
          unse_edge.insert( enc(q,e) );
          if( node[e]==-1 ){
            node[e]=node[q]+1;
            ans=max(ans,node[e]);
            que.push(e);
          }
          else if( node[e]!=node[q]+1 ){
            cout << -1 << endl;
            return 0;
          }
          
        }
      }

    }

  }

  cout << ans+1 << endl;

  return 0;

}

ll mod_pow(ll x,ll r){
  if(r==0) return 1;
  else if(r==1) return x%mod;
  else if(r%2==0){
    ll t=mod_pow(x,r/2)%mod;
    return t*t %mod;
  } 
  else{
    ll t=mod_pow(x,r/2)%mod;
    ll k= t*t %mod;
    return k*x%mod;
  } 
}
ll mod_add(ll a,ll b){
  return (a+b)%mod;
}

ll mod_mul(ll a,ll b){
  return (a*b)%mod;
}

ll mod_div(ll a,ll b){
  return mod_mul(a,mod_pow(b,mod-2));
}

void make_fact(ll n){
  fac[0]=1;
  rep(i,n){
    fac[i+1]=mod_mul(fac[i],i+1);
  }  
}

void make_invfact(ll n){
  invfac[n]= mod_pow( fac[n] ,mod-2);
  for(int i=n-1;i>=0;i--){
    invfac[i]=mod_mul(invfac[i+1],i+1);
  }

}


Measured memory_bytes: 936