#include <fstream>
#include<algorithm>
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
struct ob{
    int x,y;
}a[100001];
int n,i;
int comp(ob q,ob w)
{
    if(q.x==w.x) return q.y>w.y;
    else return q.x<w.x;
}
int main()
{
    int s=0;
    f>>n;
    for(int i=1;i<=n;i++)
        f>>a[i].x>>a[i].y;
    sort(a+1,a+n+1,comp);
    s+=a[1].y-a[1].x;
    for(i=2;i<=n;i++)
        if(a[i].x>=a[i-1].y) s+=a[i].y-a[i].x;
        g<<s;
    return 0;
}