#include "bits/stdc++.h"
using namespace std;
#ifdef _DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

//#define int long long
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define all(c) begin(c),end(c)
const int INF = sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = 1'000'000'007;
template<class T> bool chmax(T &a, const T &b) { if (a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, const T &b) { if (b < a) { a = b; return true; } return false; }

template<typename T>
vector<T> gen_v(size_t a) { return vector<T>(a); }
template<typename T, typename ...Ts>
auto gen_v(size_t a, Ts... ts) { return vector<decltype(gen_v<T>(ts...))>(a, gen_v<T>(ts...)); }
template<typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type
fill_v(T &t, const V &v) { t = v; }
template<typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type
fill_v(T &t, const V &v) { for (auto &e : t) fill_v(e, v); }

using Weight = int;
struct Edge {
	int s, d; Weight w;
	Edge() {};
	Edge(int s, int d, Weight w) : s(s), d(d), w(w) {};
};
bool operator<(const Edge &e1, const Edge &e2) { return e1.w == e2.w ? (e1.s == e2.s ? e1.d < e2.d : e1.s < e2.s) : e1.w < e2.w; }
bool operator>(const Edge &e1, const Edge &e2) { return e2 < e1; }
inline ostream &operator<<(ostream &os, const Edge &e) { return (os << '(' << e.s << ", " << e.d << ", " << e.w << ')'); }

using Edges = vector<Edge>;
using Graph = vector<Edges>;
using Array = vector<Weight>;
using Matrix = vector<Array>;

void addArc(Graph &g, int s, int d, Weight w = 1) {
	g[s].emplace_back(s, d, w);
}
void addEdge(Graph &g, int a, int b, Weight w = 1) {
	addArc(g, a, b, w);
	addArc(g, b, a, w);
}

auto getEdges = [](const Graph &g) {
	Edges ret;
	for (auto &es : g)
		for (auto &e : es)
			ret.emplace_back(e);
	return ret;
};

bool floydWarshall(const Graph &g, Matrix &dist) {
	int n = g.size();
	dist.assign(n, Array(n, INF));
	for (int i = 0; i < n; i++) dist[i][i] = 0;
	for (int i = 0; i < n; i++)
		for (auto &e : g[i])
			dist[e.s][e.d] = min(dist[e.s][e.d], e.w);
	for (int k = 0; k < n; k++)
		for (int i = 0; i < n; i++)
			for (int j = 0; j < n; j++) {
				if (dist[i][k] == INF || dist[k][j] == INF)continue;
				dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
			}
	bool negative_cycle = false;
	for (int i = 0; i < n; i++)
		if (dist[i][i] != 0)
			negative_cycle = true;
	return !negative_cycle;
}

// The diameter of a given graph
int diameter(const Graph &g) {
	Matrix dist;
	floydWarshall(g, dist);
	int n = dist.size();
	int ret = 0;
	for (int i = 0; i < n; i++)
		for (int j = 0; j < n; j++) 
			ret = max(ret, dist[i][j] == INF ? -1: (dist[i][j] + 1));
	return ret;
}

bool isBipartiteGraph(const Graph &g) {
	auto bfs = [&](const Graph &g, int s, Array &dist) {
		int n = g.size();
		vector<bool> vis(n);
		vector<int> prev(n, -1);
		dist.assign(n, INF); dist[s] = 0;
		using State = tuple<Weight, int, int>;
		queue<State> q;
		q.emplace(0, s, -1);
		while (q.size()) {
			Weight d; int v, p; tie(d, v, p) = q.front(); q.pop();
			vis[v] = true;
			prev[v] = p;
			for (auto &e : g[v]) {
				if (vis[e.d])continue;
				if (dist[e.d] > dist[v] + e.w) {
					dist[e.d] = dist[v] + e.w;
					q.emplace(dist[e.d], e.d, v);
				}
			}
		}
		return prev;
	};
	Array dist;
	bfs(g, 0, dist);
	Edges edges;
	for (auto es : g)
		edges.insert(edges.end(), es.begin(), es.end());
	for (auto e : edges)
		if (dist[e.s] % 2 == dist[e.d] % 2)
			return false;
	return true;
}

signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	int N; cin >> N;
	Graph g(N);
	rep(i, 0, N)rep(j, 0, N) {
		char c; cin >> c;
		if (c == '1') {
			addEdge(g, i, j);
		}
	}
	if (isBipartiteGraph(g)) {
		cout << diameter(g) << endl;
	}
	else {
		cout << -1 << endl;
	}
	return 0;
}

Measured memory_bytes: 2864