#include <bits/stdc++.h>
using namespace std;



typedef unsigned long ul;
typedef unsigned long long ull;
typedef long long ll;
typedef vector<ll> vint;
typedef vector< vector<ll> > vvint;
typedef vector< vector< vector<ll> > > vvvint;
typedef vector<string> vstring;
typedef vector< vector<string> > vvstring;
typedef vector<char> vchar;
typedef vector< vector<char> > vvchar;
typedef vector<long double> vdouble;
typedef vector< vector<long double> > vvdouble;
typedef vector< vector< vector<long double> > > vvvdouble;
typedef pair<ll,ll> pint;
typedef vector<pint> vpint;
typedef vector<bool> vbool;

#define rep(i,n) for(ll i=0;i<n;i++)
#define repf(i,f,n) for(ll i=f;i<n;i++)
#define repr(i,n) for(ll i=n-1;i>=0;i--)
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define pf push_front
#define fi first
#define se second
#define ALL(obj) (obj).begin(), (obj).end()
// #define LLONG_MAX 9223372036854775806
#define vmax(vec) *max_element(vec.begin(), vec.end())
#define vmin(vec) *min_element(vec.begin(), vec.end())
#define vsort(vec) sort(vec.begin(), vec.end())
#define vsortgr(vec) sort(vec.begin(), vec.end(), greater<ll>())
#define MOD 1000000007
// #define MOD 998244353
// #define MOD LLONG_MAX
const double PI=3.14159265358979323846;

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; }




int dy[]={0, 0, 1, -1};
int dx[]={1, -1, 0, 0,};



void printv(vint &v){
  for(auto e:v) cout<<e<<" ";
  cout<<endl;
}


// 繰り返し二乗法
ll power(ll a, ll b){
  if(a==1)return a;
  // if(a==0)re
  ll res=1;
  while(b>0){
    if(b&1) res=res*a%MOD;
    a=a*a%MOD;
    b>>=1;
  }
  return res;
}

const int MAX=2100000;
 
ll fact[MAX], fact_inv[MAX];
 
void init_fact(ll n){
  fact[0]=1;
  // 階乗の計算
  rep(i, n) fact[i+1]=fact[i]*(i+1)%MOD;
  fact_inv[n]=power(fact[n], MOD-2);
  // 逆元の計算
  for(ll i=n-1;i>=0;i--) fact_inv[i]=fact_inv[i+1]*(i+1)%MOD;
}
 
ll comb(ll n, ll r){
  return (fact[n]*fact_inv[r])%MOD*fact_inv[n-r]%MOD;
}
 
ll perm(ll n, ll r){
  return (fact[n]*fact_inv[n-r])%MOD;
}






int main() {
  // cout<<fixed<<setprecision(10);


  ll n; cin>>n;
  vstring s(n);
  rep(i,n) cin>>s[i];

  vvint edges(n);
  rep(i,n){
    rep(j,n){
      if(i==j) continue;
      if(s[i][j] == '0') continue;
      edges[i].push_back(j);
    }
  }

  ll ans = -1;

  auto fmp = [](ll a, ll b){
    return mp(min(a,b), max(a,b));
  };

  rep(st, n){
    vint vec(n, -1);
    vec[st] = 0;
    set<pint> used;

    queue<pint> q;
    q.push(mp(-1, st)); // par, node
    while(!q.empty()){
      ll par, node;
      tie(par, node) = q.front(); q.pop();

      for(auto to: edges[node]){
        if(to == par) continue;
        if(used.count(fmp(node, to))) continue;
        used.insert(fmp(node, to));
        if(vec[to] == -1){
          vec[to] = vec[node] + 1;
          q.push(mp(node, to));
        }else{
          if(vec[to] == vec[node] + 1){
            continue;
          }else{
            cout<<-1<<endl;
            return 0;
          }
        }
      }

    }
    chmax(ans, *max_element(ALL(vec))+1);
  }


  cout<<ans<<endl;


}






Measured memory_bytes: 1188