// #define DEBUGGING
#include <bits/stdc++.h>
#define endl '\n'
#define ALL(V) (V).begin(), (V).end()
#define ALLR(V) (V).rbegin(), (V).rend()
template <typename T> using V = std::vector<T>;
template <typename T> using VV = V<V<T>>;
using ll = std::int64_t;
using ull = std::uint64_t;
using PLL = std::pair<ll, ll>;
using TLL = std::tuple<ll, ll, ll>;
template <typename T> const T& var_min(const T &t) { return t; }
template <typename T> const T& var_max(const T &t) { return t; }
template <typename T, typename... Tail> const T& var_min(const T &t, const Tail&... tail) { return std::min(t, var_min(tail...)); }
template <typename T, typename... Tail> const T& var_max(const T &t, const Tail&... tail) { return std::max(t, var_max(tail...)); }
template <typename T, typename... Tail> void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); }
template <typename T, typename... Tail> void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); }
template <typename T> const T& clamp(const T &t, const T &low, const T &high) { return std::max(low, std::min(high, t)); }
template <typename T> void chclamp(T &t, const T &low, const T &high) { return t = clamp(t, low, high); }
namespace init__ { struct InitIO { InitIO() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << std::fixed << std::setprecision(30); } } init_io; }
#define mv_rec make_v(init, tail...)
template <typename T> T make_v(T init) { return init; }
template <typename T, typename... Tail> auto make_v(T init, size_t s, Tail... tail) { return V<decltype(mv_rec)>(s, mv_rec); }
#undef mv_rec
#ifdef DEBUGGING
#include "../../debug/debug.cpp"
#else
#define DEBUG(...) 0
#define DEBUG_SEPARATOR_LINE 0
#endif
using namespace std;

template <typename Map>
void update(Map &mp, ll key, bool inc) {
    mp[key] += inc ? 1 : -1;
    if(mp[key] == 0) mp.erase(key);
}

using Left = map<ll, ll, greater<ll>>;
using Right = map<ll, ll>;

int main() {
    ll N;
    cin >> N;
    V<PLL> LR(N);
    for(ll i = 0; i < N; i++) {
        ll l, r;
        cin >> l >> r;
        LR[i] = PLL(l - 1, r);
    }

    ll ans = 0;

    auto calc_range = [](Left &left, Right &right) {
        return max<ll>(0, right.begin()->first - left.begin()->first);
    };

    {
        Left left;
        Right right;
        for(auto &&ele : LR) {
            ll l, r;
            tie(l, r) = ele;
            update(left, l, true);
            update(right, r, true);
        }
        for(ll i = 0; i < N; i++) {
            ll l, r;
            tie(l, r) = LR[i];
            update(left, l, false);
            update(right, r, false);
            chmax(ans, (r - l) + calc_range(left, right));
            update(left, l, true);
            update(right, r, true);
        }
    }
    
    sort(ALLR(LR));

    {
        Left left_a, left_b;
        Right right_a, right_b;
        for(auto &&ele : LR) {
            ll l, r;
            tie(l, r) = ele;
            update(left_b, l, true);
            update(right_b, r, true);
        }

        for(ll i = 0; i < N - 1; i++) {
            ll l, r;
            tie(l, r) = LR[i];
            update(left_a, l, true);
            update(right_a, r, true);
            update(left_b, l, false);
            update(right_b, r, false);
            chmax(ans, calc_range(left_a, right_a) + calc_range(left_b, right_b));
        }
    }

    cout << ans << endl;
    return 0;
}


Measured memory_bytes: 14336