#include<bits/stdc++.h>
#define poly vector<int>
#define IOS ios::sync_with_stdio(false)
#define ll long long
#define mp make_pair
#define mt make_tuple
#define pa pair < int,int >
#define fi first
#define se second
#define inf 1e18
#define mod 998244353
#define sz(x) (int)((x).size())
//#define int ll
//#define N
using namespace std;
const int N=5005;
int n,l[N],r[N];
int col[N];
int lst[N];
int mth[N];
bitset<5005>f[5005];
void bfs(int k)
{
	queue<int>q;
	bitset<5005>ex;
	for (int i=1;i<=n;i++) ex[i]=1,lst[i]=0;
	q.push(k);
	while (!q.empty())
	{
		int u=q.front();q.pop();
		bitset<5005>now=(ex&f[u]);
		int v=now._Find_first();
		while (v<=n)
		{
			if (!mth[v])
			{
				int o=u;
				while (1)
				{
					int lt=mth[u];
					mth[u]=v;
					mth[v]=u;
					if (lt==0) return;
					u=lst[u];
					v=lt;
				}
			}
			else
			{
				ex[v]=0;
				now[v]=0;
				lst[mth[v]]=u;
				q.push(mth[v]);
			}
			v=now._Find_first();
		}
	}
}		
void BellaKira()
{
	cin>>n;
	for (int i=1;i<=n;i++)
		cin>>l[i]>>r[i],col[l[i]]=1;
	for (int i=1;i<=n;i++)
		for (int j=1;j<=n;j++)
			if (r[i]>l[j]&&r[i]<r[j]&&l[i]<l[j])
				f[r[i]][l[j]]=1,f[l[j]][r[i]]=1;
	n*=2;
	for (int i=1;i<=n;i++)
		if (!mth[i]&&col[i]) bfs(i);
	int ans=n;
	for (int i=1;i<=n;i++) 
		if (col[i]&&mth[i]) ans--;
	cout<<ans<<'\n';
}
signed main()
{
	IOS;
	cin.tie(0);
	int T=1;
	while (T--)
	{
		BellaKira();
	}
}