#include<bits/stdc++.h>
typedef long long ll;
#define rep(i,a,b) for(ll i=(a);i<=(b);++i)
#define per(i,a,b) for(ll i=(a);i>=(b);--i)
using namespace std;
bool Mbe;
ll read(){
	ll x=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){
		if(ch=='-')f=-1;
		ch=getchar();
	}
	while(ch>='0'&&ch<='9'){
		x=x*10+ch-'0';
		ch=getchar();
	}
	return x*f;
}
void write(ll x){
	if(x<0)x=-x,putchar('-');
	if(x>9)write(x/10);
	putchar('0'+x%10);
}
const ll N=10005,INF=1e9;
ll n,l[N],r[N],S,T,tag[N],d[N];
bitset<N>to[N];
bool bfs(){
	queue<ll>q;
	q.push(S);
	rep(i,1,T)d[i]=0;
	d[S]=1;
	while(!q.empty()){
		ll u=q.front();q.pop();
		ll v=to[u]._Find_first();
		while(v<=T){
			if(!to[u][v])break;
			if(!d[v]){
				d[v]=d[u]+1;
				q.push(v);
				if(v==T)return 1;
			}
			ll nxt=to[u]._Find_next(v);
			v=max(v+1,nxt);
		}
	}
	return 0;
}
ll dinic(ll u,ll flow){
	ll rst=flow;
	if(u==T)return flow;
	ll v=to[u]._Find_first();
	while(v<=T){
		if(!to[u][v])break;
		if(d[v]==d[u]+1){
			ll k=dinic(v,min(rst,1ll));
			if(!k)d[v]=0;
			else {
				rst--;
				to[u][v]=0,to[v][u]=1;
			}
			if(!rst)return flow;
		}
		ll nxt=to[u]._Find_next(v);
		v=max(v+1,nxt);
	}
	return flow-rst;
}
ll runflow(){
	ll res=0;
	while(bfs())res+=dinic(S,INF);
	return res;
}
bool Med;
int main(){
	cerr<<fabs(&Med-&Mbe)/1048576.0<<"MB\n";
	n=read();
	rep(i,1,n)l[i]=read(),r[i]=read(),tag[r[i]]=1;
	S=n*2+1,T=n*2+2;
	rep(i,1,n){
		rep(j,1,n){
			if(l[i]<l[j]&&l[j]<r[i]&&r[i]<r[j])to[l[j]][r[i]]=1;
		}
	}
	rep(i,1,2*n){
		if(!tag[i])to[S][i]=1;
		else to[i][T]=1;
	}
	write(2*n-runflow());
	return 0;
}