#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned long long ull;
typedef long double ld;
typedef vector<int> vi;
typedef vector<long long int> vl;
typedef vector<vector<int>> vvi;
typedef vector<vector<long long int>> vvl;
typedef pair<int, int> pii;
typedef pair<long long int, long long int> pll;
typedef vector<pair<int, int>> vii;
typedef vector<pair<long long int, long long int>> vll;
#define fast() ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define test() long long int t; cin >> t; cin.ignore(); while(t--) 
#define ff first
#define ss second
#define pb push_back
#define pf push_front
#define mp make_pair
#define MOD 1000000007
#define SMOD 998244353
#define pq priority_queue
#define all(x) x.begin(),x.end()
#define SP(x) setprecision(x)
#define sp " "
#define inp(a) ll a;cin>>a;cin.ignore()
#define inps(a,b) ll a,b;cin>>a>>b;cin.ignore()
#define out(a) cout<<SP(20)<<a<<'\n'
#define outs(a,b) cout<<SP(20)<<a<<" "<<b<<'\n'
#define ins insert
#define er erase
#define lb lower_bound
#define ub upper_bound
#define printclock cerr<<"Time : "<<1000*(ld)clock()/(ld)CLOCKS_PER_SEC<<"ms\n";
#define inpa(a,n) ll a[n]; for(int i=0; i<n; i++){cin>>a[i];}
#define inpv(a,n) vl a; for(int i=0; i<n; i++){inp(x);a.pb(x);}
#define outa(a,n) for(int i=0;i<n;i++){cout<<a[i]<<" ";}cout<<'\n';
#define outv(v) for(auto i:v){cout<<i<<" ";}cout<<'\n';
set<char> vow = {'a','e','i','o','u','A','E','I','O','U'};
ll xpow(ll n, ll m){if(m==0){return 1;}else{ll x = xpow(n, m/2);if(m&1){return x*x*n;}else{return x*x;}}}
ll xmod(ll a, ll m){return (((a%m)+m)%m);}
ll xmodpow(ll n, ll m, ll y){if(m==0){return 1;}else{ll x = xmodpow(n, m/2, y);if(m&1){return xmod((xmod((xmod(x,y)*xmod(x,y)),y)*xmod(n,y)),y);}else{return xmod((xmod(x,y)*xmod(x,y)),y);}}}

bool check;
int col[1005];
bool vis1[1005];
vl g[1005];

void dfs(ll i){
    vis1[i]=1;
    for(auto j:g[i]){
        if(!vis1[j]){
            if(col[i]==1){
                col[j]=2;
            }
            else{
                col[j]=1;
            }
            dfs(j);
        }
        else{
            if(col[j]==col[i]){
                check = 1;
            }
        }
    }
}

int main(){
    fast();

/* you get what you work for not what you wish for */
    inp(n);
    for (int i=0; i<n; i++){
        string s;
        cin >> s;
        for(int j=0; j<n; j++){
            if(s[j]-'0'){
                g[i].pb(j);
                g[j].pb(i);
            }
        }
    }
    col[0]=1;
    dfs(0);
    if(check){
        cout << -1 << endl;
        return 0;
    }
    ll ans = 1;
    for(int i=0; i<n; i++){
        bool vis[n+5]={0};
        vis[i]=1;
        queue <int> q;
        q.push(i);
        int lev[n+5]={0};
        int par[n+5];
        lev[i]=1;
        par[i]=-1;
        while(!q.empty()){
            int j = q.front();
            q.pop();
            for(auto k:g[j]){
                if(vis[k]){
                    continue;
                }
                else{
                    vis[k]=1;
                    lev[k] = lev[j]+1;
                    par[k]=j;
                    ans = max(ans, (ll)lev[k]);
                    q.push(k);
                }
            }
        }
    }
    out(ans);
}

Measured memory_bytes: 1152