#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
using i64 = int64_t;
#define rep(i, j, n) for(int i = (j); i < (n); ++i)

vector<vector<int>> d;
vector<int> color;


bool dfs(int v = 0, int c = 1) {
	color[v] = c;
	rep(nv, 0, d[v].size()) {
		if (d[v][nv] == 1) {
			if (color[nv] == c) return false;
			if (color[nv] == 0 && !dfs(nv, -c)) return false;
		}
	}
	return true;
}


int main() {
	cin.tie(0);
	ios_base::sync_with_stdio(0);

	int n; cin >> n;
	int ans = 0;
	char c;
	d.resize(n, vector<int>(n, 1 << 29));
	color.resize(n, 0);
	rep(i, 0, n) {
		rep(j, 0, n) {
			cin >> c;
			if (c == '1') d[i][j] = 1;
		}
		d[i][i] = 0;
	}
	if (!dfs()) {
		cout << -1;
		return 0;
	}
	
	rep(k, 0, n) rep(i, 0, n) rep(j, 0, n) d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
	rep(i, 0, n) rep(j, 0, n) {
		ans = max(ans, d[i][j]);
	}
	cout << ans + 1;

	return 0;
}