#include<bits/stdc++.h>
using namespace std;
const int inf=1e9;
inline int read(){
	int x=0,f=1;char ch=getchar();
	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}
	while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
	return x*f;
}
int n,S,T,dep[10005];bitset<10005>g[10005];
int bfs(){
	for(int i=1;i<=T;i++)dep[i]=0;
	dep[S]=1;queue<int>q;q.push(S);
	while(!q.empty()){
		int u=q.front();q.pop();
		for(int v=g[u]._Find_first();v<=T;v=max(v+1,(int)g[u]._Find_next(v))){
			if(g[u][v]==0)continue;
			if(!dep[v])dep[v]=dep[u]+1,q.push(v);
		}
	}
	return dep[T];
}
int dinic(int u,int flow){
	if(u==T)return flow;
	int rest=0;
	for(int v=g[u]._Find_first();v<=T&&flow;v=max(v+1,(int)g[u]._Find_next(v))){
		if(g[u][v]==0)break;
		if(dep[v]!=dep[u]+1)continue;
		int k=dinic(v,min(flow,1));if(!k)dep[v]=0;
		rest+=k,flow-=k;if(k)g[u][v]=0,g[v][u]=1;
	}
	return rest;
}
int l[5005],r[5005],pos[10005];
signed main(){
	n=read(),S=2*n+1,T=2*n+2;
	for(int i=1;i<=n;i++){
		l[i]=read(),r[i]=read();
		pos[l[i]]=0,pos[r[i]]=1;
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			if(l[i]<l[j]&&l[j]<r[i]&&r[i]<r[j]){
				g[l[j]][r[i]]=1;
			}
		}
	}
	for(int i=1;i<=2*n;i++)if(pos[i]==0)g[S][i]=1;
	for(int i=1;i<=2*n;i++)if(pos[i]==1)g[i][T]=1;
	int ans=2*n;
	while(bfs())ans-=dinic(S,inf);
	printf("%d\n",ans);	
	return 0;
}