#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("int.in");
ofstream g("int.out");
struct virgula{
int x,y;
}v[1000001],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 a,i,nr,n;
int main()
{
f>>n;

for(i=1;i<=n;i++)
{
    f>>v[i].x>>v[i].y;
}
sort(v+1,v+n+1,cmp);
a=v[1].y;
nr=a-v[1].x;
for(i=2;i<=n;i++)
{
    if(a<=v[i].x)
    {
        a=v[i].y;
        nr=nr+v[i].y-v[i].x;
    }
}
g<<nr;
    return 0;

}