#include<bits/stdc++.h>
using namespace std;using ll=long long;using vi=vector<int>;using vvi=vector<vi>;using vl=vector<ll>;using vvl=vector<vl>;using P=pair<int,int>;using PL=pair<ll,ll>;using vp=vector<P>;using vpl=vector<PL>;
template<typename T>constexpr auto inf=numeric_limits<T>::max()/2;constexpr int INF=inf<int>,MOD=1000000007;constexpr ll LINF=inf<ll>;
#define _ol3(_1,_2,_3,name,...)name
#define _rep(i,n)_repi(i,0,n)
#define _repi(i,a,b)for(int i=a,i##_l=(b);i<i##_l;++i)
#define REP(...)_ol3(__VA_ARGS__,_repi,_rep,)(__VA_ARGS__)
#define REPR(i,n)for(int i=n-1;i>=0;--i)
#define REPA(i,v)REP(i,(v).size())
#define all(v)(v).begin(),(v).end()
#define rall(v)(v).rbegin(),(v).rend()
#define bit(n)(1ll<<(n))
#define F first
#define S second
#define endl '\n'
#define cho(n,a,b)cout<<((n)?a:b)<<endl
void YES(int n){cho(n,"YES","NO");}void Yes(int n){cho(n,"Yes","No");}void Poss(int n){cho(n,"Possible","Impossible");}
void _print(ostream&){}template<class T,class...U>void _print(ostream&s,const T&t,const U&...u){s<<t<<(sizeof...(u)?' ':'\n');_print(s,u...);}
template<class...T>void print(const T&...t){_print(cout,t...);}template<class...T>void dprint(const T&...t){_print(cerr,t...);}
#ifndef LOCAL
struct osd{template<class T>osd&operator<<(const T&t){return*this;}};osd cer_;
#define dprint(...)
#define cerr cer_
#endif
template<class T>bool chmax(T&a,const T&b){bool x=a<b;x?a=b:b;return x;}template<class T>bool chmin(T&a,const T&b){bool x=a>b;x?a=b:b;return x;}
template<class T,class U>ostream&operator<<(ostream&o,const pair<T,U>&p){return o<<p.F<<' '<<p.S;}
template<class T,class U>istream&operator>>(istream&i,pair<T,U>&p){return i>>p.F>>p.S;}
template<class T>class iterable{static false_type c(string v);template<class U>static auto c(U v)->decltype(all(v),true_type());static false_type c(...);public:const static bool value=decltype(c(declval<T>()))::value;};
template<class T,typename=enable_if_t<iterable<T>::value>>ostream&operator<<(ostream&o,const T&v){for(auto&&i:v)o<<i<<' ';return o;}
template<class T>istream&operator>>(istream&i,vector<T>&v){for(T&j:v)i>>j;return i;}
template<class T>vector<T>&operator<<(vector<T>&v,const T&t){v.push_back(t);return v;}
template<class T>set<T>&operator<<(set<T>&v,const T&t){v.insert(t);return v;}
template<class T>multiset<T>&operator<<(multiset<T>&v,const T&t){v.insert(t);return v;}

// 解説を読んだ.がんばってとけなかったのになんでレートが落ちたのか考えると悔しさのようなものを感じている
// いや天才解法じゃん?なんでRecommendationsでProabilityが58%なんですか,キレている
// 凡ミスで1ペナ生やしてキレている(575)
// 誰だよ前回Pythonで出したままPythonで出し続けてREを生やしたやつ,出てこい

int main(){
    cin.tie(0);ios::sync_with_stdio(0);
    cout<<setprecision(10);
    int n;
    cin>>n;
    vector<set<int>> es(n);
    vvi g(n, vi(n,INF));
    REP(i,n){
        g[i][i]=0;
        string s;
        cin>>s;
        REP(j,n){
            if(s[j]=='1'){
                g[i][j]=1;
                es[i].insert(j);
            }
        }
    }
    REP(i,n)dprint(es[i]);
    vi c(n, -1);
    queue<int> q;
    q.push(0);
    c[0]=0;
    while(q.size()){
        const int x=q.front();
        q.pop();
        for(int a:es[x]){
            dprint(c);
            dprint(x,'-',a);
            if(c[a]!=-1){
                if(c[a]==c[x]){
                    cout<<-1<<endl;
                    return 0;
                }
                continue;
            }
            c[a]=1-c[x];
            q.push(a);
        }
    }
    int ma=0;
    REP(i,n)dprint(g[i]);
    REP(k,n){
        REP(i,n){
            REP(j,n){
                chmin(g[i][j], g[i][k]+g[k][j]);
            }
        }
    }
    REP(i,n){
        dprint(g[i]);
        REP(j,n)if(g[i][j]!=INF)chmax(ma, g[i][j]);
    }
    cout<<ma+1<<endl;
}


Measured memory_bytes: 2304