#include <fstream>
#include <algorithm>

using namespace std;

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

const int N = 100001;

int n, d[N];
pair <int, int> v[N];

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

int cautbin(int x) {
    int r = 0, pas = 1 << 28;

    while (pas != 0) {
        if (r + pas < x && v[r + pas].second <= v[x].first) {
            r += pas;
        }
        pas >>= 1;
    }

    return r;
}

int main()
{
    in >> n;
    for (int i = 1; i <= n; i++) in >> v[i].first >> v[i].second;
    in.close();

    sort(v + 1, v + n + 1, cond);
    for (int i = 1; i <= n; i++) d[i] = max(d[i - 1], v[i].second - v[i].first + d[cautbin(i)]);

    out << d[n];
    out.close();
}