#include <bits/stdc++.h>
#define INF 1000000000
#define LINF 1000000000000000000
#define MOD 1000000007
#define mod 998244353
#define F first
#define S second
#define ll int
#define N 5010
using namespace std;
ll n,col,mat[N*2],vid[N*2];
pair<ll,ll> p[N];
bitset<N*2> nei[N*2];
bool dfs(ll x)
{
	ll i;
	vid[x]=col;
	for(i=nei[x]._Find_first();i<N*2;i=nei[x]._Find_next(i))
	{
		if(mat[i]==-1)
		{
			mat[x]=i,mat[i]=x;
			return true;
		}
		if(vid[i]!=col&&dfs(i))
		{
			mat[x]=i,mat[i]=x;
			return true;
		}
	}
	return false;
}
ll solve()
{
	ll i,ret=0;
	for(i=0;i<n*2;i++)
	{
		mat[i]=-1;
	}
	col=0;
	while(true)
	{
		col++;
		ll cnt=0;
		for(i=0;i<n;i++)
		{
			if(mat[i]==-1&&dfs(i))
			{
				cnt++;
			}
		}
		if(cnt==0)
		{
			break;
		}
		ret+=cnt;
	}
	return ret;
}
int main(){
	ll i;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		scanf("%d%d",&p[i].F,&p[i].S);
	}
	sort(p,p+n);
	set<pair<ll,ll> > alls;
	for(i=0;i<n;i++)
	{
		while(!alls.empty())
		{
			if((*alls.begin()).F>=p[i].F)
			{
				break;
			}
			alls.erase(alls.begin());
		}
		for(set<pair<ll,ll> >::iterator it=alls.begin();it!=alls.end()&&(it->F)<p[i].S;it++)
		{
			nei[i][(it->S)+n]=nei[(it->S)+n][i]=1;
		}
		alls.insert(make_pair(p[i].S,i));
	}
	printf("%d\n",n*2-solve());
	return 0;
}