#include "bits/stdc++.h"
using namespace std;
#define Rep(i,n) for(int i=0;i<(int)(n);i++)
#define For(i,n1,n2) for(int i=(int)(n1);i<(int)(n2);i++)
#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define RREP(i,n) for(ll i=((ll)(n)-1);i>=0;i--)
#define FOR(i,n1,n2) for(ll i=(ll)(n1);i<(ll)(n2);i++)
#define RFOR(i,n1,n2) for(ll i=((ll)(n1)-1);i>=(ll)(n2);i--)
#define all(a)  (a).begin(),(a).end()
#define SORT(a) sort((a).begin(),(a).end())
#define oorret 0
#define oor(x) [&](){try{x;} catch(const out_of_range& oor){return oorret;} return x;}()
#define IOS cin.tie(0),ios::sync_with_stdio(false)
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
template<typename T1, typename T2> inline bool chmin(T1& a, T2 b) { if (a > b) { a = b; return 1; }return 0; }
template<typename T1, typename T2> inline bool chmax(T1& a, T2 b) { if (a < b) { a = b; return 1; }return 0; }
template<class Type>struct is_vector : std::false_type {};
template<class ValueType, class Alloc>struct is_vector<std::vector<ValueType, Alloc>> : std::true_type {};
template <typename T> inline ostream& operator << (ostream& out, const vector<T>& v) {
    if (v.empty())return out;
    constexpr bool is_vector_v = is_vector<T>::value;
    if (is_vector_v)for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? "\n" : "");
    else for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? " " : "");
    return out;
}
inline void put() {}
template<class T> inline void put(const T& first) { std::cout << first << "\n"; }
template<class T, class... N> inline void put(const T& first, const N& ... rest) { std::cout << first << " "; put(rest...); }
inline void putn() {}
template<class T, class... N> inline void putn(const T& first, const N& ... rest) { std::cout << first << "\n"; putn(rest...); }

class Bipartite{
public:
    vector<vector<int>> path;
    vector<int> res;
    Bipartite(int n,vector<vector<int>> &path):path(path){
        res.resize(n);
        fill(all(res),-1);
    }
    
    bool judge(){
        return dfs(this->path,this->res,0,0);
    }
    bool dfs(vector<vector<int>>& path,vector<int>&res,int now,int color){
        res[now]=color;
        REP(i,path[now].size()){
            int next=path[now][i];
            if(res[next]==color){
                return false;
            }
            if(res[next]==-1&&!dfs(path,res,next,1-color)){
                return false;
            }
        }
        return true;
    }
};

int main() {
    IOS;
    int n;
    cin >> n;
    vector<string> s(n);
    vector<vector<int>> path(n);
    REP(i,n){
        cin >> s[i];
    }
    vector<vector<int>> e(n,vector<int>(n,1e6));//infで初期化
    Rep(i,n){
        Rep(j,n){
            if(s[i][j]=='1'){
                e[i][j] = 1;
                path[i].push_back(j);
                path[j].push_back(i);
            }
        }
    }
    REP(i,n){
       e[i][i]=0;
    }
    Bipartite b(n,path);
    if(!b.judge()){
        put(-1);
        return 0;
    }
    //wf
    REP(k,n){
       REP(i,n){
           REP(j,n){
               chmin(e[i][j],e[i][k]+e[k][j]);
           }
       }
    }
    
    int res = 0;
    REP(i,n){
        REP(j,n){
            chmax(res,e[i][j]);
        }
    }
    put(res+1);
    return 0;
}


Measured memory_bytes: 1152