#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
struct heavy
{
    int s,f;
};
heavy v[105];
bool cmp(heavy a,heavy b)
{
    if(a.f<b.f)
        return 1;
    else
        return 0;
}
int n,i,fina,nr;
int main()
{
    f>>n;
    for(i=1;i<=n;i++)
    {
        f>>v[i].s>>v[i].f;
    }
    sort(v+1,v+n+1,cmp);
    nr=v[1].f-v[1].s;fina=v[1].f;
    for(i=2;i<=n;i++)
    {
        if(v[i].s>=fina)
            {
                fina=v[i].f;
                nr+=v[i].f-v[i].s;
            }
    }
    g<<nr;
    return 0;
}