#include<cstdio>

#include<iostream>

#include<cstdlib>

#include<cstring>

#include<cmath>

#include<vector>

using namespace std;

const int maxn=100;

bool g[maxn][maxn],found;

int ans,list[maxn][maxn],n,len[maxn],mc[maxn];

void dfs(int size)

{

 int i,j,k;

 if(len[size]==0)

 	{

 	 if(size>ans)

 	 	{

 	 	 ans=size;

 	 	 found=true;

		}

	 return ;

	}

 for( k=0;k<len[size]&&!found;++k)

 	{

 	 if(size+len[size]-k<=ans)break;

 	 int i=list[size][k];

 	 if(size+mc[i]<=ans)break;

 	 for(j=k+1,len[size+1]=0;j<len[size];++j)

 	 	{

 	 	 if(g[i][list[size][j]])

 	 	 	list[size+1][len[size+1]++]=list[size][j];

		}

	 	 dfs(size+1);

	}

}

void max_cluster()

{

 int i,j;

 mc[n]=ans=1;

 for(int i=n-1;i>0;--i)

 	{

 	 found=false;len[1]=0;

 	 for(int j=i+1;j<=n;++j)

 	 	if(g[i][j])list[1][len[1]++]=j;

 	 dfs(1);

 	 mc[i]=ans;

	}

}

int main()

{

 freopen("t.txt","r",stdin);

 while(scanf("%d",&n))

 	{

 	 if(!n)return 0;

 	 memset(g,0,sizeof(g));

 	 memset(mc,0,sizeof(mc));

 	 memset(list,0,sizeof(list));

 	 for(int i=1;i<=n;i++)

 	 	for(int j=1;j<=n;j++)

 	 	    {

 	 	     int t;scanf("%d",&t);

 	 	     if(t==1)g[i][j]=1;

			}

 	 max_cluster();

 	 printf("%d\n",ans);

	}

 return 0;

}