#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template <class T> using treap = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
using Int = long long;
#define REP(i, n) for (long long i = 0, max_i = (n); i < max_i; i++)
#define REPI(i, a, b) for (long long i = (a), max_i = (b); i < max_i; i++)
#define ALL(obj) begin(obj), end(obj)
#define RALL(obj) rbegin(obj), rend(obj)
#define fi first
#define se second
using ii = pair<Int, Int>;
vector<ii> dirs = {
    {1, 0}, {0, 1}, {-1, 0}, {0, -1},  // 4方向
    {1, 1}, {-1, 1}, {-1, -1}, {1, -1},  // 斜め
    {0, 0},  // 自身
};
Int get_msb(long long x) {
    assert(x != 0);
    return 63 - __builtin_clzll(x);
}
Int get_lsb(long long x) {
    assert(x != 0);
    return __builtin_ctzll(x);
}
template <class T> inline bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } return false; }
template <class T> inline bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; } return false; }
template <class T, class S> vector<T> make_vec(size_t n, S x) { return vector<T>(n, x); }
template <class T, class... Ts> auto make_vec(size_t n, Ts... ts) { return vector<decltype(make_vec<T>(ts...))>(n, make_vec<T>(ts...)); }

// debug
template <class T> ostream& operator<<(ostream& s, const vector<T>& d) { REP (i, d.size()) s << d[i] << (i == d.size() - 1 ? "" : " "); return s; }
template <class T> ostream& operator<<(ostream& s, const vector<vector<T>>& d) { REP (i, d.size()) s << d[i] << (i == d.size() - 1 ? "" : "\n"); return s; }
template <class T, class S> ostream& operator<<(ostream& s, const pair<T, S>& p) { s << "{" << p.first << ", " << p.second << "}"; return s; }
template <class T> ostream& operator<<(ostream& s, const set<T> m) { for (auto it = m.begin(); it != m.end(); it++) { s << *it << (next(it) == m.end() ? "" : "\n"); } return s; }
template <class T> ostream& operator<<(ostream& s, const multiset<T> m) { for (auto it = m.begin(); it != m.end(); it++) { s << *it << (next(it) == m.end() ? "" : "\n"); } return s; }
template <class T, class S> ostream& operator<<(ostream& s, const map<T, S> m) { for (auto it = m.begin(); it != m.end(); it++) { s << *it << (next(it) == m.end() ? "" : "\n"); } return s; }
template <class T, class S> ostream& operator<<(ostream& s, const unordered_map<T, S> m) { for (auto it = m.begin(); it != m.end(); it++) { s << *it << (next(it) == m.end() ? "" : "\n"); } return s; }
#ifdef _MY_DEBUG
    #define dump(...) cerr << "/* " << #__VA_ARGS__ << " :[" << __LINE__ << ":" << __FUNCTION__ << "]" << endl, dump_func(__VA_ARGS__), cerr << "*/\n\n";
#else
    #define dump(...)
    #define endl "\n"
#endif
void dump_func() { cerr << endl; }
template <class Head, class... Tail> void dump_func(Head&& h, Tail&&... t) { cerr << h << (sizeof...(Tail) == 0 ? "" : ", "), dump_func(forward<Tail>(t)...); }

struct FastIO { FastIO() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); } } fast_io;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
constexpr Int MOD = 1000000007;
// **********************************************************************************************
// **********************************************************************************************
// **********************************************************************************************
// **************************************** TEMPLATE END ****************************************
// **********************************************************************************************
// **********************************************************************************************
// **********************************************************************************************

constexpr Int INF = 1e18;
signed main() {
    Int n; cin >> n;
    vector<ii> ps(n);
    REP (i, n) cin >> ps[i].fi >> ps[i].se;
    sort(ALL(ps));

    Int ma1 = 0;
    {
        vector<Int> mil(n + 1, INF), mir(n + 1, INF);
        vector<Int> mal(n + 1, -1), mar(n + 1, -1);
        REP (i, n) {
            mil[i + 1] = min(mil[i], ps[i].se);
            mal[i + 1] = max(mal[i], ps[i].fi);
        }
        for (Int i = n - 1; i >= 0; i--) {
            mir[i] = min(mir[i + 1], ps[i].se);
            mar[i] = max(mar[i + 1], ps[i].fi);
        }
        REP (i, n) {
            Int l = max(mal[i], mar[i + 1]);
            Int r = min(mil[i], mir[i + 1]);
            chmax(ma1, ps[i].se - ps[i].fi + 1 + max(0LL, r - l + 1));
        }
    }
    Int ma2 = 0;
    {
        vector<ii> use;
        for (ii p : ps) {
            while (use.size() && use.back().se >= p.se) use.pop_back();
            use.push_back(p);
        }
        REP (i, (Int)use.size() - 1) {
            Int a = max(0LL, use[0].se - use[i].fi + 1);
            Int b = max(0LL, use[i + 1].se - use.back().fi + 1);
            chmax(ma2, a + b);
        }
    }
    cout << max(ma1, ma2) << endl;
}


Measured memory_bytes: 4992