#include      <fstream>
#include      <algorithm>

using namespace std;

ifstream in("heavymetal.in");
ofstream out("heavymetal.out");

struct spectacol {
	int inceput;
	int final;
	int durata;
} v[101], g[101];

bool comp(spectacol a, spectacol b) {
	return (a.durata > b.durata);
}

int n;

int main() {

	ios::sync_with_stdio(false);
	in.tie(NULL), out.tie(NULL);
	
	in >> n;
	for (int i = 1; i <= n; i++) {
		in >> v[i].inceput >> v[i].final;
		v[i].durata = v[i].final - v[i].inceput;
	}

	sort(v + 1, v + n + 1, comp);

	int k = 1, nr = v[1].durata;
	g[1] = v[1];
	for (int i = 2; i <= n; i++) if (g[k].inceput >= v[i].final)g[++k] = v[i], nr += v[i].durata;
	out << nr;

    return 0;

}