#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((lint)(x).size())
#define POW2(n) (1LL << (n))
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> bool mmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T> bool mmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; }
template<typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template<typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
///// This part below is only for debug, not used /////
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const deque<T> &vec){ os << "deq["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa){ os << "(" << pa.first << "," << pa.second << ")"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;
///// END /////
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/tag_and_trait.hpp>
using namespace __gnu_pbds; // find_by_order(), order_of_key()
template<typename TK> using pbds_set = tree<TK, null_type, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename TK, typename TV> using pbds_map = tree<TK, TV, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
*/

int main()
{
    int N;
    cin >> N;
    vector<plint> LR(N), RL(N);
    lint ret = 0;
    REP(i, N)
    {
        cin >> LR[i].first >> LR[i].second;
        RL[i] = make_pair(LR[i].second, LR[i].first);
        mmax(ret, LR[i].second - LR[i].first + 1);
    }
    sort(ALL(LR));
    sort(ALL(RL));
    lint lmax = LR.back().first;
    lint rmin = RL[0].first;
    // dbg(lmax);
    // dbg(rmin);
    lint offset = 0;
    bool flg = false;
    if (lmax <= rmin)
    {
        lint shift = rmin - lmax + 1;
        offset += shift * 2;
        REP(i, N)
        {
            if (LR[i].first >= rmin) LR[i].first -= shift;
            else if (LR[i].first >= lmax) LR[i].first = lmax;

            if (LR[i].second >= rmin) LR[i].second -= shift;
            else if (LR[i].second >= lmax) LR[i].second = lmax - 1;
        }
        rmin = lmax - 1;
        flg = true;
    }
    // dbg(offset);
    // dbg(LR);

    // if (lmax > rmin)
    // dbg("A");
    vector<plint> v;
    for (auto p : LR) v.emplace_back(max(rmin - p.first + 1, 0LL), max(p.second - lmax + 1, 0LL));
    sort(ALL(v));
    // REP(i, v.size()) v[i].second *= -1;
    // dbg(v);

    // dbg(v);

    lint ret2 = 0;
    vector<lint> acm(v.size());
    acm[0] = v[0].second;
    REP(i, N - 1) acm[i + 1] = min(acm[i], v[i + 1].second);
    REP(i, N - 1)
    {
        mmax(ret2, acm[i] + v[i + 1].first);
    }
    if (flg) REP(i, N) mmax(ret2, v[i].first + v[i].second);

    // else
    // {
    //     // dbg("B");
    //     vector<plint> v;
    //     for (auto p : LR) v.emplace_back(max(p.second - rmin + 1, 0LL), max(lmax - p.first + 1, 0LL));
    //     sort(ALL(v));
    //     reverse(ALL(v));
    //     // dbg(v);
    //     vector<plint> vacc = v;
    //     IREP(i, (int)v.size() - 1)
    //     {
    //         mmin(vacc[i].first, v[i + 1].first);
    //         mmin(vacc[i].second, v[i + 1].second);
    //     }
    //     plint vv = v[0];
    //     dbg(v);
    //     dbg(vacc);
    //     REP(i, N - 1)
    //     {
    //         mmin(vv.first, v[i].first);
    //         mmin(vv.second, v[i].second);
    //         mmax(ret, vv.first + vv.second + vacc[i + 1].first + vacc[i + 1].second + (rmin - lmax - 1) * 2);
    //     }
    // }
    cout << max(ret, ret2 + offset) << endl;
}


Measured memory_bytes: 5744