#include <map>
#include <iostream>
#include <algorithm>
#include <vector>
#include <fstream>
using namespace std;

int lower_bound_value(int t, const map<int, int>& dp) {
    auto lb = dp.lower_bound(t);
    if (lb != dp.end()) {
        if (lb->first > t) {
            lb--;
        }
    } else {
        lb--;
    }
    if (lb->first > t)
        return 0;
    return lb->second;
}

int main() {
    typedef pair<int, int> interval;
    ifstream fin("heavymethal.in");
    ofstream fout("heavymethal.out");
    int n;
    fin >> n;
    vector<pair<int,int>> intervals(n);
    for (int i = 0; i < n; i++)
        fin >> intervals[i].first >> intervals[i].second;

    sort(intervals.begin(), intervals.end(),
            [](const interval& i1, const interval& i2) {
                return i1.second < i2.second;
            });

    map<int, int> dp;
    dp.insert(make_pair(intervals[0].second, intervals[0].second - intervals[0].first));
    for (int i = 1; i < n; i++) {
        int previous_value = lower_bound_value(intervals[i].first, dp);
        int current_value = lower_bound_value(intervals[i].second, dp);
        auto current = dp.find(intervals[i].second);
        if (current != dp.end()) {
            current->second = max(current->second,
                    previous_value + intervals[i].second - intervals[i].first);
        } else {
            dp.insert(make_pair(intervals[i].second,
                        max(current_value, previous_value + intervals[i].second - intervals[i].first)));
        }
    }
    fout << dp.rbegin()->second << endl;
    return 0;
}