#include <bits/stdc++.h>
 
using namespace std;
 
typedef long long ll;
typedef pair<ll,ll> P;
 
long long int INF = 3e18;
double Pi = 3.1415926535897932384626;
 
vector<ll> G[550010];
//vector<P> tree[500010];
priority_queue <ll> pql;
priority_queue <P> pqp;
//big priority queue
priority_queue <ll,vector<ll>,greater<ll> > pqls;
priority_queue <P,vector<P>,greater<P> > pqps;
//small priority queue
//top pop
 
int dx[8]={1,0,-1,0,1,1,-1,-1};
int dy[8]={0,1,0,-1,1,-1,-1,1};
char dir[] = "DRUL";
//ll bit[500005];
//↓,→,↑,←
 
 
#define p(x) cout<<x<<"\n";
#define el cout<<endl;
#define pe(x) cout<<(x)<<" ";
#define ps(x) cout<<fixed<<setprecision(25)<<x<<endl;
#define pu(x) cout<<(x);
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define CLEAR(a) a = decltype(a)(); 
 
 
ll mod = 1000000007;

ll rui(ll number1,ll number2){

    if(number2 == 0){
        return 1;
    }else{
        ll number3 = rui(number1,number2 / 2);
        number3 *= number3;
        number3 %= mod;
        if(number2%2==1){
            number3 *= number1;
            number3 %= mod;
        }
        return number3;
    }
}
ll gcd(ll number1,ll number2){
 
    if(number1 > number2){
        swap(number1,number2);
    }
    if(number1 == 0 || number1 == number2){
        return number2;
    }else{
        return gcd(number2 % number1,number1);
    }
}
void YES(bool condition){
 
    if(condition){
        p("YES");
    }else{
        p("NO");
    }
    return;
}
void Yes(bool condition){
 
    if(condition){
        p("Yes");
    }else{
        p("No");
    }
    return;
}

/*
ll fact[800005],rfact[800005];

void c3_init(){
    fact[0] = rfact[0] = 1;
    for(ll i=1; i<=800000; i++){
        fact[i] = (fact[i-1]*i) % mod;
    }
    rfact[800000] = rui(fact[800000],mod - 2);
    for(ll i=800000; i>=1; i--){
       rfact[i-1] = rfact[i] * i;
       rfact[i-1] %= mod;
    }
    return;}
ll c3(ll n,ll r){
    return (((fact[n] * rfact[r]) % mod ) * rfact[n-r]) % mod;}
*/
 
ll n,m,num,sum,a,b,c,d,e,g,h,w,i,j,q,r,l;
ll k,ans;
ll x[500005],y[500005],z[500005];
char s[5005][5005];
ll color[50000];

//char s[500005];

bool dfs(ll v,ll c){
    color[v] = c;
    for(int i=0;i<G[v].size();i++){
        ll nv = G[v][i];
        if(color[nv] == c)return false;
        if(color[nv] == 0 && !dfs(nv, 3 - c))return false;
    }
    return true;
}


int main(){
    cin >> n;
    for(int i=0;i<n;i++){
        cin >> s[i];
        for(int j=0;j<n;j++){
            if(s[i][j] == '1'){
                G[i].pb(j);
            }
        }
    
    }
    if(!dfs(0,1)){
        p(-1);
        return 0;
    }

    for(int i=0;i<n;i++){
        x[i] = -1;
        y[i] = -1;
    }
    ll ans = 0;
    for(int i=0;i<n;i++){
        queue<ll> q;
        for(int j=0;j<n;j++){
            x[j] = INF;
        }
        q.push(i);
        x[i] = 0;
        while(!q.empty()){
            ll v = q.front();
            q.pop();
            for(int k=0;k<G[v].size();k++){
                ll nv = G[v][k];
                if(x[nv] == INF){
                    q.push(nv);
                    x[nv] = x[v] + 1;
                }
            }
        }        

        for(int j=0;j<n;j++){
            if(x[j] > ans)ans = x[j];
        }
    }
    p(ans + 1);

    return 0;
}

















Measured memory_bytes: 20096