#include <iostream>
#include <queue>
#include <cstring>
#include <cmath>
#include <cstdio>
#include <vector>
using namespace std;
typedef pair<int,int> ii;
const int N=5e5+20;
const int inf=1e9;
struct node{
	int to,next,w;
}e[N];
int head[N],cnt;
void insert(int u,int v,int w)
{
	e[cnt].to=v,e[cnt].w=w,e[cnt].next=head[u];
	head[u]=cnt++;
}
int n,inq[N],d[N];
queue<int> q;
void SPFA(int s,int t)
{
	while(!q.empty())
		q.pop();
	for(int i=0;i<=s;i++)
		inq[i]=0,d[i]=inf;
	q.push(s);
	inq[s]=1,d[s]=0;
	while(!q.empty())
	{
		int u=q.front();
		q.pop(),inq[u]=0;
		for(int i=head[u];i!=-1;i=e[i].next)
		{
			int v=e[i].to,w=e[i].w;
			if(d[v]>d[u]+w)
			{
				d[v]=d[u]+w;
				if(!inq[v])
					inq[v]=1,q.push(v);
			//	cout<<v<<‘ ‘<<d[v]<<endl;
			}
		}
	}
	cout<<d[s]-d[t]<<endl;
}
int main()
{
	int w=2,a,b;
	while(cin>>n)
	{
		//d[b]-d[a-1]>=2
		//d[a-1]<=d[b]+(-2)
		cnt=0;
		memset(head,-1,sizeof(head));
		int mx=-inf,mn=inf;
		for(int i=1;i<=n;i++)
		{
			scanf("%d%d",&a,&b);
		
			insert(b+1,a,-2);
			mx=max(mx,b+1),mn=min(mn,a);
		}
		//d[i+1]<=d[i]+1
		//d[i]<=d[i+1]
		
		for(int i=0;i<mx;i++)
			insert(i,i+1,1),insert(i+1,i,0);
	//	cout<<mx<<‘ ‘<<mn-1<<endl;
		SPFA(mx,mn);	
	
	}
	return 0;
}