import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.range, std.typecons;
import std.numeric, std.math, std.random;
import core.bitop;

string FMT_F = "%.10f";

static string[] s_rd;
T RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
string RDR()() { return readln.chomp; }
T[] ARR(T = long)(in string str, T fix = 0) { auto r = str.split.to!(T[]); r[] += fix; return r; }
T[] RDA(T = long)(T fix = 0) { auto r = readln.chomp.split.to!(T[]); r[] += fix; return r; }
T[][] RDA2(T = long)(size_t n, T[] fix = []) { auto r = new T[][](n); foreach (i; 0..n) { r[i] = readln.chomp.split.to!(T[]); foreach (j, e; fix) r[i][j] += e; } return r; }
size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
long lcm(long x, long y) { return x * (y / gcd(x, y)); }

long mod = 10^^9 + 7;
//long mod = 998244353;
//long mod = 1_000_003;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }

void main()
{
	auto N = RD;
	auto edges = new long[][](N);
	foreach (i; 0..N)
	{
		auto S = RD!string;
		foreach (j, c; S)
		{
			if (c == '1')
			{
				edges[i] ~= j;
			}
		}
	}
	/*while (true){
	auto N = 5;
	auto S = new char[][](N, N);
	foreach (i; 0..N)
	{
		auto num = uniform(0, N-1);
		if (i != 0)
		{
			auto pos = uniform(0, i);
			S[i][pos] = '1';
			S[pos][i] = '1';
		}
		foreach (j; 0..num)
		{
			auto pos = i;
			while (pos == i)
			{
				pos = uniform(0, N);
			}
			S[i][pos] = '1';
			S[pos][i] = '1';
		}
	}
	auto edges = new long[][](N);
	foreach (i; 0..N)
	{
		foreach (j, c; S[i])
		{
			if (c == '1')
			{
				edges[i] ~= j;
			}
		}
	}
	foreach (i; 0..N)
	{
		foreach (to; edges[i])
			writeln(i, " ", to);
	}
	long _ans = -1;
	foreach (i1; 0..N)
	{
		foreach (i2; 0..N)
		{
			foreach (i3; 0..N)
			{
				foreach (i4; 0..N)
				{
					foreach (i5; 0..N)
					{
						auto list = [i1, i2, i3, i4, i5];
						auto set = new bool[](N);
						foreach (e; list)
							set[e] = true;
						long cnt;
						foreach (e; set)
							if (e) ++cnt;
						if (cnt <= _ans) continue;

						auto close = new bool[](N);
						bool dfs(long from, long par)
						{
							if (close[from]) return true;
							close[from] = true;
							foreach (to; edges[from])
							{
								if (to == par) continue;
								if (list[to] == list[from]-1 || list[to] == list[from]+1)
								{
									auto r = dfs(to, from);
									if (!r) return false;
								}
								else
									return false;
							}
							return true;
						}
						auto r = dfs(0, 0);
						if (r)
						{
							_ans = cnt;
							debug writeln(list);
						}
					}
				}
			}
		}
	}
	debug writeln("ans:", _ans);*/

	long bfs(long pos)
	{
		long[2][] open = [[pos, -1]];
		auto dist = new long[](N);
		dist[] = -1;
		dist[pos] = 0;
		while (!open.empty)
		{
			auto n = open.front; open.popFront;
			auto from = n[0];
			auto par  = n[1];
			foreach (to; edges[from])
			{
				if (to == par) continue;
				if (dist[to] != -1)
				{
					auto diff = dist[from]+1 - dist[to];
					if (diff != 0 && diff != 2)
						return -1;

					continue;
				}
				dist[to] = dist[from] + 1;
				open ~= [to, from];
			}
		}
		long p = dist.MIN_POS!"a > b"();
		debug writeln("dist:", dist);
		return dist[p]+1;
	}

	long ans = -1;
	foreach (i; 0..N)
	{
		auto r = bfs(i);
		debug writeln(r);
		/*if (r == -1)
		{
			ans = -1;
			break;
		}*/
		ans = max(ans, r);
	}

	writeln(ans);
	//if (_ans != ans) break;
	stdout.flush();
	debug readln();
}

Measured memory_bytes: 1916