#include <fstream>
#include <algorithm>

using namespace std;

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

int n, d[100001], poz[100001];
pair <int, int> v[100001];

bool cond(int i, int j) {
    return (v[i].second < v[j].second);
}

inline int lung(int k) {
    return v[poz[k]].second - v[poz[k]].first;
}

int cautbin(int x) {
    int pas = 1 << 17, r = 0;
    while (pas != 0) {
        if (r + pas <= n && v[poz[r + pas]].second <= x) {
            r += pas;
        }
        pas >>= 1;
    }
    return r;
}

int main()
{
    in >> n;
    for (int i = 1; i <= n; i++) {
        in >> v[i].first >> v[i].second;
        poz[i] = i;
    }
    sort(poz + 1, poz + n + 1, cond);

    d[1] = lung(1);
    for (int i = 2; i <= n; i++) {
        d[i] = max(d[i - 1], d[cautbin(v[poz[i]].first)] + lung(i));
    }
    out << d[n];
}