#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");

struct form
{
    int a,b;
}v[100001];

int compare(form a,form b)
{
    if(a.a!=b.a)return (a.b<b.b);
    else return (a.b>=b.b);
}
int main()
{
    int i,n,u=1,s=0;
    f>>n;
    for(i=1;i<=n;i++)
        f>>v[i].a>>v[i].b;
    sort(v+1,v+n+1,compare);
    s=s+v[1].b-v[1].a;
    for(i=2;i<=n;i++)
    {
        if(v[i].a>=v[u].b)
        {
            s=s+v[i].b-v[i].a;
            u=i;
        }
    }
    g<<s;
    return 0;
}