#include <bits/stdc++.h>
#define rep(i, n) for(int i=0; i<(n); ++i)
#define rep2(i, s, n) for(int i=s; i<(n); ++i)
#define ALL(v) (v).begin(), (v).end()

using namespace std;

typedef long long ll;

static const int INTINF = (2147483647 >> 1); // 10^9 + 5000
static const ll LLINF = (9223372036854775807 >> 1);
static const int MAX = 1e5+1;
static const ll MOD = 1e9+7;

namespace Kunitaka{
    template<
        typename TYPE,
        std::size_t SIZE
    >
    std::size_t array_length(const TYPE (&array)[SIZE])
    {
        return SIZE;
    }
}
using namespace Kunitaka;
namespace Printer{
    void br(){
        cout << endl;
    }

    void loop_cnt(int i){
        cout << "i = " << i << endl;
    }

    void loop_cnt(int i, int j){
        cout << "i = " << i << ", " << "j = " << j << endl;
    }

    template<class T>
    void print(T x){
        cout << x << endl;
    }

    template<class T, class S>
    void print(T x, S y){
        cout << x << "," << y << endl;
    }

    template<class T, class S, class U>
    void print(T x, S y, U z){
        cout << x << "," << y << "," << z << endl;
    }

    template<class T, class S>
    void print(pair<T, S> p){
        cout << p.first << ", " << p.second << endl;
    }

    template<
        typename TYPE,
        std::size_t SIZE
    >
    void print(const TYPE (&array)[SIZE]){
        int lim = array_length(array);
        for(int i=0; i<lim; i++){
            if(i) cout << " ";
            cout << array[i];
        }
        cout << endl;
    }

    template<class S>
    void print(vector<S> v){
        for(int i=0; i<v.size(); i++){
            if(i) cout << " ";
            cout<< v[i];
        }
        cout << endl;
    }

    template<class S>
    void print(vector<vector<S> > vv){
        for(int i=0; i<vv.size(); i++){
            for(int j=0; j<vv[i].size(); j++){
                if(j) cout << " ";
                cout << vv[i][j];
            }
            cout << endl;
        }
    }

    void yesno(bool x){
        if(x) cout << "Yes" << endl;
        else cout << "No" << endl;
    }
};
using namespace Printer;

const int MAX_V = 300;
vector<int> G[MAX_V]; // 入力
int V;

int color[MAX_V]; // 頂点iの色

bool detect(int s, int c){
    color[s] = c;
    for(int u : G[s]){
        if(color[u] == color[s]) return false;
        if(color[u] != 0) continue;
        if(!detect(u, c * -1)) return false;
    }
    return true;
}





int main(int argc, const char * argv[]) {
    //提出時、消す----//


    // input
    cout << fixed << setprecision(10);
    cin >> V;
    rep(i, V){
        string str; cin >> str;
        rep(j, str.size()){
            if(str[j] == '1'){
                if(i == j){
                    cout << "-1" << endl;
                    return 0;
                }
                G[i].push_back(j);
            }
        }
    }
    fill(color, color+MAX_V, 0);

    // variable
    ll ans = 0;
    // solve
    ans = detect(0, 1);
    if(!ans) {
        cout << -1 << endl;
        return 0;
    }

    vector<vector<int> > d(MAX_V, vector<int>(MAX_V));
    rep(i, V){
        rep(j, V){
            d[i][j] = INTINF;
        }
        for(int u : G[i]){
            d[i][u] = 1;
        }
        d[i][i] = 0;
    }

    for(int k=0; k<V; k++){
        for(int i=0; i<V; i++){
            for(int j=0; j<V; j++){
                d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
            } 
        }
    }

    ans = 0;
    rep(i, V){
        ans = max((int)ans, *max_element(ALL(d[i])));
    }


    print(ans + 1);

    return 0;
}


Measured memory_bytes: 768