#include<iostream>

#include<stdio.h>

#include<string.h>

#include<algorithm>

using namespace std;

struct node

{

	int x1,y1,x2,y2;

}s[1100];

int dp[1100],vist[1100][1100],n;

int dfs(int num)

{

	if(dp[num]>0)

	return dp[num];

	dp[num]=1;

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

	{

		if(vist[num][i])

		{

			int tmp=dfs(i)+1;

			if(tmp>dp[num])

			dp[num]=tmp;

		}

	}

	return dp[num];

}

int main()

{

	while(scanf("%d",&n)>0&&n)

	{

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

		{

			int x1,y1,x2,y2;

			scanf("%d%d%d%d",&x1,&y1,&x2,&y2);

			s[i].x1=x1;

			s[i].y1=y1;

			s[i].x2=x2;

			s[i].y2=y2;

		}

		memset(dp,0,sizeof(dp));

		memset(vist,0,sizeof(vist));

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

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

		{

			if(s[i].x2<s[j].x1&&s[i].y2<s[j].y1)

			vist[i][j]=1;

		}

		int maxx=0;

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

		{

			int tmp=dfs(i);

			if(tmp>maxx)

			maxx=tmp;

		}

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

	}

	return 0;

}