#include <fstream>
#include <algorithm>
using namespace std;
ifstream in("heavymetal.in");
ofstream out("heavymetal.out");
struct ceva
{
    int x,y;
}a[100005];
bool crit(ceva p1, ceva p2)
{
    if(p1.x<p2.x) return true;
    else if(p1.x==p2.x && p1.y>p2.y) return true;
    else return false;
}
long long n,i,mx,cont;
int main()
{
    in>>n;
    for(i=1;i<=n;i++)
        in>>a[i].x>>a[i].y;
    sort(a+1,a+n+1,crit);
    for(i=1;i<=n;i++) if(a[i].x>=mx)
    {
        mx=a[i].y;
        cont+=a[i].y-a[i].x;
    }
    out<<cont;
    return 0;
}