#define _CRT_SECURE_NO_WARNINGS
#define _SCL_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <iostream>
#include <string>
#include <vector>
#include <list>
#include <utility>
#include <algorithm>
#include <functional>
#include <cmath>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <iomanip>
#include <sstream>
#include <bitset>
#include <limits>
#include <numeric>
#include <valarray>
#include <fstream>
#include <array>
#include <random>
#include <unordered_set>
#include <unordered_map>

using namespace std;
using uint = unsigned int;
using LL = long long;
using ULL = unsigned long long;
using PP = pair<LL, LL>;
template <typename T> using PriorityQ = priority_queue<T, vector<T>, greater<T> >;
#define REP(i, a, n) for(LL i = (a), i##_max = (n); i < i##_max; ++i)
#define REM(i, a, n) for(LL i = (LL)(n) - 1, i##min = (a); i >= i##min; --i)
#define FLOAT fixed << setprecision(16)
#define SPEEDUP { cin.tie(NULL); ios::sync_with_stdio(false); }
const int INF = 0x3FFFFFFF;
const LL INFLL = 0x3FFFFFFF3FFFFFFF;
const double INFD = 1.0e+308;
const double EPS = 1.0e-9;

void YesNo(bool b) { cout << (b ? "Yes" : "No") << endl; }
void YESNO(bool b) { cout << (b ? "YES" : "NO") << endl; }
template <class T, class U> istream& operator>>(istream& ist, pair<T, U>& right) { return ist >> right.first >> right.second; }
template <class T, class U> ostream& operator<<(ostream& ost, const pair<T, U>& right) { return ost << right.first << ' ' << right.second; }
template <class T, class TCompatible, size_t N> void Fill(T(&dest)[N], const TCompatible& val) { fill(dest, dest + N, val); }
template <class T, class TCompatible, size_t M, size_t N> void Fill(T(&dest)[M][N], const TCompatible& val) { for (int i = 0; i < M; ++i) Fill(dest[i], val); }
template <class T> T Next() { T buf; cin >> buf; return buf; }
istream& Ignore(istream& ist) { string s; ist >> s; return ist; }
bool Inside(int i, int j, int h, int w) { return i >= 0 && i < h && j >= 0 && j < w; }

#ifdef ONLY_MY_ENVIR
#include "IntMod.h"
#include "BinaryMatrix.h"
#include "BIT.h"
#include "Factorization.h"
#include "FlowSolver.h"
#include "Graph.h"
#include "LazySegmentTree.h"
#include "Math.h"
#include "Matrix.h"
#include "MinMax.h"
#include "Position.h"
#include "Range.h"
#include "Rational.h"
#include "SegmentTree.h"
#include "SegmentTree2D.h"
#include "SuffixArray.h"
#include "Tree.h"
#include "UnionFind.h"
#include "MinCostFlowSolver.h"
#include "Bipartite.h"
#include "FFT.h"
#endif

#ifdef __GNUC__
typedef __int128 LLL;
istream& operator>> (istream& ist, __int128& val) { LL tmp;  ist >> tmp; val = tmp; return ist; }
ostream& operator<< (ostream& ost, __int128 val) { LL tmp = val; ost << tmp; return ost; }
#endif

int N;
vector<int> G[200];
int C[200];

int D[200][200];
int Dist() {
	Fill(D, INF);
	REP(i, 0, N) {
		D[i][i] = 0;
		for (int j : G[i]) {
			D[i][j] = 1;
			D[j][i] = 1;
		}
	}

	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]);
			}
		}
	}

	int mx = 0;
	REP(i, 0, N) {
		REP(j, 0, N) {
			mx = max(mx, D[i][j]);
		}
	}
	return mx;
}


bool rec(int from, int c) {
	if (C[from] != 0) {
		if (C[from] == c) return true;
		if (C[from] != c) return false;
	}
	C[from] = c;

	for (int to : G[from]) {
		if (!rec(to, -c)) return false;
	}
	return true;
}

bool isBipartite() {
	return rec(0, 1);
}

int main() {
	cin >> N;
	REP(i, 0, N) {
		string S;
		cin >> S;
		REP(j, 0, N) {
			if (S[j] == '1') {
				G[i].push_back(j);
			}
		}
	}

	if (isBipartite()) {
		cout << Dist() + 1 << endl;
	} else {
		cout << -1 << endl;
	}

	return 0;
}



Measured memory_bytes: 512