#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=210,inf=1e9;
int d[N][N],v[N],s[N];
signed main()
{
	int n;cin>>n;
	for(int i=1;i<=n;i++)for(int j=1;j<=n;j++)scanf("%1lld",&d[i][j]);
	deque<int>q;q.push_back(1);v[1]=0;
	while(!q.empty())
	{
		int x=q.front();q.pop_front();
		for(int j=1;j<=n;j++)if(d[x][j])
		{
			if(!v[j])v[j]=1,s[j]=s[x]^1,q.push_back(j);
			else if(s[j]==s[x])
			{
				cout<<-1;
				return 0;
			}
		}
	}
	for(int i=1;i<=n;i++)for(int j=1;j<=n;j++)if(i!=j&&d[i][j]==0)d[i][j]=inf;
	for(int k=1;k<=n;k++)for(int i=1;i<=n;i++)for(int j=1;j<=n;j++)
		if(i!=j&&j!=k&&i!=k)
			d[i][j]=min(d[i][j],d[i][k]+d[k][j]);
	int ans=0;
	for(int i=1;i<=n;i++)for(int j=1;j<=n;j++)ans=max(ans,d[i][j]);
	cout<<ans+1;
	return 0;
}