#include <iostream>
#include <iomanip>
#include <string>
#include <stack>
#include <vector>
#include <math.h>
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <map>
#include <set>
#include <queue>
#include <list>
using namespace std;
using pii  = pair<int,int>;
using ll=long long;
using ld=long double;
#define pb push_back
#define mp make_pair
#define stpr setprecision
#define rep(i,n) for(ll i=0;i<(n);++i)
#define REP(i,a,b) for(ll i=(a);i<(b);++i)
#define crep(i) for(char i='a';i<='z';++i)
#define psortsecond(A,N) sort(A,A+N,[](const pii &a, const pii &b){return a.second<b.second;});
#define ALL(x) (x).begin(),(x).end()
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define endl '\n'
int ctoi(const char c){
  if('0' <= c && c <= '9') return (c-'0');
  return -1;
}
ll gcd(ll a,ll b){return (b == 0 ? a : gcd(b, a%b));}
ll lcm(ll a,ll b){return a*b/gcd(a,b);}
constexpr ll MOD=1000000007;
constexpr ll INF=1000000011;
constexpr ll MOD2=998244353;
constexpr ll LINF = 1001002003004005006ll;
constexpr ld EPS=10e-8;
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; }
template<typename T> istream& operator>>(istream& is,vector<T>& v){for(auto&& x:v)is >> x;return is;}
template<typename T,typename U> istream& operator>>(istream& is, pair<T,U>& p){ is >> p.first; is >> p.second; return is;}
template<typename T,typename U> ostream& operator>>(ostream& os, const pair<T,U>& p){ os << p.first << ' ' << p.second; return os;}
template<class T> ostream& operator<<(ostream& os, vector<T>& v){
    for(auto i=begin(v); i != end(v); ++i){
        if(i !=begin(v)) os << ' ';
        os << *i;
    }
    return os;
}

struct  UndirectedGraph{
    vector<vector<int>> g;   //グラフの各点が持つ枝の情報
    vector<int> clr;         //グラフの持つ枝の情報
    vector<int> dis;         //距離の情報
    int V;

    UndirectedGraph(int V) : V(V),
    g(vector<vector<int>>(V)),
    clr(vector<int>(V,0))
    {}

    //don't add (v,u) after adding (u,v)
    void add_edge(int u,int v){
        g[u].push_back(v);
        g[v].push_back(u);
    }


    //二部グラフ判定
    bool dfs_nib(int v,int c){
        clr[v]=c;
        for(auto x:g[v]){
            if(clr[x]==c) return false;
            if(clr[x]==0 && !dfs_nib(x,-c) ) return false;
        }
        return true;
    }
    bool isNib(){
        bool ret=true;
        for(int i=0;i<V;i++)if(clr[i]==0){
            if(!dfs_nib(i,1)){
                ret=false;break;
            }
        }
        return ret;
    }

    //distance
    void bfs(int st){
        dis=vector<int>(V,INF);
        vector<bool> checked(V,false);
        dis[st]=0;
        queue<int> q;
        q.push(st);
        while(!q.empty()){
            auto now=q.front();q.pop();
            //ここでもcontinueしないとダブる
            if(checked[now]) continue;
            checked[now]=true;
            for(auto x:g[now]){
                if(checked[x]) continue;
                dis[x]=dis[now]+1;
                q.push(x);
            }
        }
    }
};

signed main(){
    int n;
    cin>>n;
    UndirectedGraph g(n);
    char s[n][n];
    rep(i,n){
        rep(j,n){
            char t;cin>>t;
            s[i][j]=t;
            if(t=='1'&&i>j){
                g.add_edge(i,j);
            }
        }
    }
    if(!g.isNib()){
        cout<<-1<<endl;
        return 0;
    }

    int ans=0;
    rep(i,n){
        g.bfs(i);
        int x=*max_element(ALL(g.dis));
        ans=max(x,ans);
    }   
    cout<<ans+1<<endl;
    return 0;
}


Measured memory_bytes: 512