#include <fstream>
#include <algorithm>
using namespace std;
ifstream f ("heavymetal.in");
ofstream g ("heavymetal.out");
int const NM = 1e5 + 1;
pair <int , int> v [NM];
bool crt (pair <int , int> a , pair <int , int> b){
    if (a . first == b . first)
        return a . second > b . second;
    return a . first < b . first;
}
int main()
{
    int n;
    f >> n;
    for(int i = 1 ; i <= n ; ++ i)
        f >> v [i] . first >> v [i] . second;
    sort (v + 1 , v + 1 + n , crt);
    int p = 1 , ans = 0;
    pair <int , int> e = v [1];
    ans = e . second - e . first;
    while (p <= n){
        if (v [p] . first >= e . second)
            e = v [p] , ans += e . second - e . first;
        ++ p;
    }
    g << ans;
    return 0;
}