// clang-format off
#include<bits/stdc++.h>
#define pb push_back
#define P make_pair
#define fi first
#define se second
#define bit(s,x) (((s)>>(x))&1)
#define pnp(s) __builtin_popcountll(s)
#define rep(i,a,b) for(int i=(a);i<=(b);++i)
#define per(i,a,b) for(int i=(a);i>=(b);--i)
using namespace std;
typedef long long ll; 
typedef unsigned long long ull; 
typedef pair<int,int> pii; typedef pair<ll,int> pli; typedef pair<ll,ll> pll; typedef pair<int,ll> pil;
inline ll read(){
	ll x=0,f=1,c=getchar();
	while(c<'0'||c>'9')f=(c=='-'?-1:1),c=getchar();
	while(c>='0'&&c<='9')x=(x<<1)+(x<<3)+(c^48),c=getchar();
	return x*f;
}
const int N=5e3+3;
// clang-format on
int n,mh[N],mh2[N],pre[N];
pii p[N];
bitset<N>to[N],vis;
inline bool bfs(int s){
	queue<int>q;vis.set();q.push(s);int t=0;
	while(!q.empty()&&!t){
		int u=q.front();q.pop();
		bitset<N>tmp = vis&to[u];
		for(int j=tmp._Find_first();j<=n;j=tmp._Find_next(j)){
			int v=mh2[j];vis[j]=0;pre[j]=mh[u];
			if(!v){t=j;break;}
			else q.push(v);
		}
	}if(!t)return 0;
	for(int v=t;v;v=pre[v]){
		if(pre[v])mh2[v]=mh2[pre[v]],mh[mh2[v]]=v;
		else mh[s]=v,mh2[v]=s;
	}
	return 1;
}
int main() {
    //freopen("data.in", "r", stdin);
    // freopen(".in","r",stdin);
    // freopen("myans.out","w",stdout);
	n=read();rep(i,1,n)p[i].fi=read(),p[i].se=read();
	rep(i,1,n)rep(j,1,n)if(p[i].fi<p[j].fi&&p[j].fi<p[i].se&&p[i].se<p[j].se)to[i][j]=1;
	int ans=0;rep(i,1,n)ans += bfs(i);
	cout<<n*2-ans;
    return 0;
}