#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
int i,n,aux,k,s;
struct heavy
{
    int  x,y;
} v[100001];
int  cmp(heavy a,  heavy b)
{
    return a.y <b.y;
}

int main()
{
    f>>n;
    for(i=1; i<=n; i++)
        f>>v[i].x>>v[i].y;
    sort(v + 1, v + n + 1, cmp);
    for(i = 1; i <= n; ++ i)
if(v[i].x>aux)
        {
            if(v[i].x==v[i+1].x&&v[i+1].y-v[i+1].x>v[i].y-v[i].x)

             s=s+(v[i+1].y-v[i+1].x);
            else s=s+(v[i].y-v[i].x);
            aux=v[i].y;
        }
g<<s;

    return 0;
}