// #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;

const ll inf = 5e15;

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

    {
        sort(ALL(lr_lis));
        auto ite = unique(ALL(lr_lis));
        lr_lis.erase(ite, lr_lis.end());
    }

    auto get_id = [&](ll x) {
        return distance(lr_lis.begin(),
                        lower_bound(ALL(lr_lis), x));
    };

    auto get_range = [&](ll l, ll r) {
        return max<ll>(0, lr_lis[r] - lr_lis[l]);
    };

    ll ans = 0;
    V<ll> lcnt(lr_lis.size()), rcnt(lr_lis.size());
    ll max_l = -inf, min_r = inf;
    for(auto &&ele : LR) {
        ll l, r;
        tie(l, r) = ele;
        l = get_id(l);
        r = get_id(r);
        ele = PLL(l, r);
        lcnt[l]++;
        rcnt[r]++;
        chmax(max_l, l);
        chmin(min_r, r);
    }

    {
        for(ll i = 0; i < N; i++) {
            ll l, r;
            tie(l, r) = LR[i];
            lcnt[l]--;
            rcnt[r]--;
            ll left = [&] { for(ll i = max_l;; i--) if(lcnt[i]) return i; }();
            ll right = [&] { for(ll i = min_r;; i++) if(rcnt[i]) return i; }();
            chmax(ans, get_range(l, r) + get_range(left, right));
            lcnt[l]++;
            rcnt[r]++;
        }
    }
    
    sort(ALLR(LR));

    {
        ll max_l2 = -inf, min_r2 = inf;
        for(ll i = 0; i < N - 1; i++) {
            ll l, r;
            tie(l, r) = LR[i];
            chmax(max_l2, l);
            chmin(min_r2, r);
            lcnt[l]--;
            rcnt[r]--;
            for(;; max_l--) if(lcnt[max_l]) break;
            for(;; min_r++) if(rcnt[min_r]) break;
            chmax(ans, get_range(max_l, min_r) + get_range(max_l2, min_r2));
        }
    }

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


Measured memory_bytes: 6640