#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;
ifstream f ("heavymetal.in");
ofstream g ("heavymetal.out");
int i,n,dr,st,s;
struct virgula
{
    int x,y;
}v[10001],o,p;
int cmp (virgula o, virgula p)
{
    if (o.x<p.x)
       return 1;
    if (o.x==p.x&&o.y>p.y)
       return 1;
    return 0;
}

int main()
{
    f>>n;
    for(i=1;i<=n;i++)
    {
        f>>v[i].x>>v[i].y;
    }
    sort (v+1,v+n+1,cmp);
    dr=v[1].y;
    st=v[1].x;
    s=1;
    s=v[1].y-v[1].x+1;
    for (i=2;i<=n;i++)
    {
        if(v[i].x>=dr){
          s=v[i].y-v[i].x-1+s;

          dr=v[i].y;}
    }
    g<<s;
    return 0;
}