// poj1716

#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstring>

#include<cstdio>

#include<cmath>

#include<queue>

#define LL long long

#define inf 2147483640

#define Pi acos(-1.0)

#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);

using namespace std;

inline LL getint() {

    int f,x=0;char ch=getchar();

    while (ch<='0' || ch>'9') {if (ch=='-') f=-1;else f=1;ch=getchar();}

    while (ch>='0' && ch<='9') {x=x*10+ch-'0';ch=getchar();}

    return x*f;

}

const int maxn=10010;

struct edge {int next,to,w;}e[maxn<<2];

int head[maxn],vis[maxn],dis[maxn],cnt,s,t,n;

void link(int u,int v,int w) {

    e[++cnt].to=v;e[cnt].next=head[u];head[u]=cnt;e[cnt].w=w;

}

void SPFA() {

    queue<int> q;

    while (q.size()) q.pop();

    for (int i=s;i<=t;i++) {

        vis[i]=1;

        dis[i]=0;

        q.push(i);

    }

    while (q.size()) {

        int x=q.front();

        q.pop();

        vis[x]=0;

        for (int i=head[x];i;i=e[i].next)

            if (dis[e[i].to]<dis[x]+e[i].w) {

                dis[e[i].to]=dis[x]+e[i].w;

                if (!vis[e[i].to]) {

                    q.push(e[i].to);

                    vis[e[i].to]=1;

                }

            }

    }

}

int main() {

    scanf("%d",&n);

    s=inf,t=0;

    for (int x,y,i=1;i<=n;i++) {

        scanf("%d%d",&x,&y);

        link(x,y+1,2);

        s=min(s,x);

        t=max(t,y+1);

    }

    for (int i=s;i<=t;i++) link(i-1,i,0),link(i,i-1,-1);

    SPFA();

    printf("%d",dis[t]);

    return 0;

}