#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
int s,n,i;
struct spec{
int x,y;
int o;

}a[100005];
int compare(spec u,spec v){
    if (u.y==v.y) return u.x<v.x;
return u.y<v.y;
}
int main()
{f>>n;
for(i=1;i<=n;i++){
    f>>a[i].x>>a[i].y;
    a[i].o=i;

}
sort(a+1,a+n+1,compare);
i=1;
int mmax=1,u=n;
s=a[n].y-a[n].x;
    for(i=n-1;i>=1;i--){
      if(a[u].x>=a[i].y){
    u=i;
s+=a[u].y-a[u].x;
      }


    }
    g<<s;
      return 0;
}