#include <bits/stdc++.h>
using namespace std;

constexpr int INF = numeric_limits<int>::max() / 4;

#define REP(i, stop) FOR(i, 0, stop)
#define FOR(i, start, stop) for (int i = start, i##_len = stop; i < i##_len; ++i)

signed main() {
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	int N;
	cin >> N;
	vector<string> S(N);
	REP(i, N) cin >> S[i];
	vector<vector<int>> d(N, vector<int>(N));
	REP(i, N) REP(j, N) {
		d[i][j] = i == j ? 0 : S[i][j] == '1' ? 1 : INF;
	}
	REP(k, N) REP(i, N) REP(j, N) {
		int *ij = &d[i][j];
		int *ik = &d[i][k];
		int *kj = &d[k][j];
		if (*ik == INF) continue;
		if (*kj == INF) continue;
		if (*ij == INF) {
			*ij = *ik + *kj;
		} else {
			if ((*ij + *ik + *kj) & 1 == 1) {
				cout << -1 << endl;
				return 0;
			}
			if (*ij > *ik + *kj) {
				*ij = *ik + *kj;
			}
		}
	}
	int ans = 0;
	REP(i, N) REP(j, N) {
		if (d[i][j] != INF)
			ans = max(ans, d[i][j]);
	}
	cout << ans + 1 << endl;
}
