#include <fstream>
#include <algorithm>

using namespace std;

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

pair <int, int> v[100005];
int p, i, j, n, st, dr, d[100005];

bool comp (pair <int, int> a, pair <int, int> b){
    return a.second < b.second;
}

int main(){
	fin >> n;
	for(i=1; i<=n; i++)
		fin >> v[i].first >> v[i].second;
	sort (v + 1, v + n + 1, comp);
    d[1] = v[1].second - v[1].first;
    for (i=2; i<=n; i++){
        st = 1;
        dr = i - 1;
        p = 0;
        while (st <= dr){
            int mid = (st + dr)/2;
            if (v[i].first >= v[mid].second){
                st = mid + 1;
                p = mid;
            }
            else{
                dr = mid - 1;
            }
        }
        d[i] = max (d[i-1], d[p] + (v[i].second - v[i].first));
    }
    fout << d[n];
	return 0;
}