#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Edge = int;
using Graph = vector<vector<Edge>>;
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define SORT(v) sort((v).begin(), (v).end())
#define RSORT(v) sort((v).rbegin(), (v).rend())
const ll MOD = 1000000007;
const ll nmax = 200;
const ll INF = 1e9;
bool graph[nmax][nmax];
vector<vector<ll>> dist = vector<vector<ll>>(nmax, vector<ll>(nmax, INF));
void warshall_floyd(ll n)
{
    for (size_t i = 0; i < n; i++)
    {
        for (size_t j = 0; j < n; j++)
        {
            for (size_t k = 0; k < n; k++)
            {
                dist[j][k] = min(dist[j][k], dist[j][i] + dist[i][k]);
            }
        }
    }
}

class UnionFind
{
public:
    vector<ll> Parent;

    UnionFind(ll N)
    {
        Parent = vector<ll>(N, -1);
    }
    ll find(ll A)
    {
        if (Parent[A] < 0)
            return A;
        return Parent[A] = find(Parent[A]);
    }

    ll size(ll A)
    {
        return -Parent[find(A)];
    }

    bool Union(ll A, ll B)
    {
        A = find(A);
        B = find(B);
        if (A == B)
        {
            return false;
        }
        if (size(A) < size(B))
            swap(A, B);

        Parent[A] += Parent[B];
        Parent[B] = A;

        return true;
    }
};

ll gcd(ll a, ll b)
{
    if (b == 0)
        return a;
    return gcd(b, a % b);
}

ll lcm(ll a, ll b)
{
    ll g = gcd(a, b);
    return a / g * b;
}

ll mulMod(ll a, ll b)
{
    return (((a % MOD) * (b % MOD)) % MOD);
}

ll powMod(ll a, ll p)
{
    if (p == 0)
    {
        return 1;
    }
    else if (p % 2 == 0)
    {
        ll half = powMod(a, p / 2);
        return mulMod(half, half);
    }
    else
    {
        return mulMod(powMod(a, p - 1), a);
    }
}

ll ceil(ll a, ll b)
{
    return (a + b - 1) / b;
}
long long N;
vector<int> seen(N, 0);
bool can = true;
void dfs(const Graph &G, int v, int cnt)
{
    if (seen[v] == 0)
    {
        seen[v] = cnt; // v を訪問済にする
    }
    else
    {
        if (seen[v] != cnt)
        {
            can = false;
        }
    }

    // v から行ける各頂点 next_v について
    for (auto next_v : G[v])
    {
        if (seen[next_v] != 0)
        {
            if (seen[next_v] != cnt - 1 && seen[next_v] != cnt + 1)
            {
                can = false;
            }
            continue;
        }
        dfs(G, next_v, cnt + 1); // 再帰的に探索
    }
}

int main()
{

    scanf("%lld", &N);
    Graph G(N);
    for (int i = 0; i < N; i++)
    {
        string tmp;
        cin >> tmp;
        for (int j = 0; j < N; j++)
        {
            if (tmp[j] != '0')
            {
                G[i].push_back(j);
                dist[i][j] = 1;
            }
        }
    }

    for (int i = 0; i < N; i++)
    {
        dist[i][i] = 0;
    }

    warshall_floyd(N);
    int maximum = 0;
    pair<int, int> edge;
    for (int i = 0; i < N; i++)
    {
        for (int j = 0; j < N; j++)
        {
            if (dist[i][j] > maximum)
            {
                edge = make_pair(i, j);
                maximum = dist[i][j];
            }
        }
    }
    seen.assign(N, 0);

    queue<int> que;

    que.push(edge.first);

    while (!que.empty())
    {
        int v = que.front();
        que.pop();
        for (int next_v : G[v])
        {
            if (seen[next_v] != 0)
            {
                if (seen[next_v] != seen[v] - 1 && seen[next_v] != seen[v] + 1)
                {
                    can = false;
                }
                continue;
            }

            seen[next_v] = seen[v] + 1;
            que.push(next_v);
        }
    }

    if (can)
    {
        cout << maximum + 1 << endl;
    }
    else
    {
        cout << -1 << endl;
    }

    return 0;
}


Measured memory_bytes: 768