#if __has_include("../library/Basic/Debug.hpp")

#include "../library/Basic/Debug.hpp"

#else

/* ----- Header Files ----- */
// IO
#include <cstdio>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm
#include <algorithm>
#include <cmath>
#include <numeric>

// container
#include <vector>
#include <array>
#include <string>
#include <tuple>
#include <complex>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <bitset>

// others
#include <random>
#include <limits>
#include <functional>
#include <ctime>
#include <cassert>
#include <cstdint>

/* ----- Type Alias ----- */
using lint = long long int;
using ldouble = long double;
template <class T>
using MaxHeap = std::priority_queue<T>;
template <class T>
using MinHeap = std::priority_queue<T, std::vector<T>, std::greater<T>>;

template <class T>
T ndvec(T v) { return v; }

template <class T, class... Ts>
auto ndvec(size_t l, Ts... ts) {
    return std::vector<decltype(ndvec<T>(ts...))>(l, ndvec<T>(ts...));
}

template <class Cost = int>
struct Edge {
    int src, dst;
    Cost cost;
    Edge(int src = -1, int dst = -1, Cost cost = 1)
        : src(src), dst(dst), cost(cost){};

    bool operator<(const Edge<Cost>& e) const { return this->cost < e.cost; }
    bool operator>(const Edge<Cost>& e) const { return this->cost > e.cost; }
};

template <class Cost = int>
using Edges = std::vector<Edge<Cost>>;
template <class Cost = int>
using Graph = std::vector<std::vector<Edge<Cost>>>;

#endif

/* ----- Misc ----- */
void fastio() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
}

struct Fout {
    int precision;
    explicit Fout(int precision) : precision(precision) {}
};

std::ostream& operator<<(std::ostream& os, const Fout& fio) {
    os << std::fixed << std::setprecision(fio.precision);
    return os;
}

/* ----- Constants ----- */
// constexpr int INF = std::numeric_limits<int>::max() / 3;
// constexpr int MOD = 1000000007;
// const Real PI = acos(-1);
// constexpr Real EPS = 1e-10;
// std::mt19937 mt(int(std::time(nullptr)));

struct Seg {
    int l, r;
    int len() {
        return std::max(0, r - l + 1);
    }
};

int main() {
    int n;
    std::cin >> n;

    std::vector<Seg> segs(n);
    for (auto& s : segs) {
        std::cin >> s.l >> s.r;
    }

    std::sort(segs.begin(), segs.end(),
              [](const Seg& a, const Seg& b) {
                  return a.r != b.r ? a.r < b.r : a.l < b.l;
              });
    // r最小，l最小を持ってくる
    auto base = segs.front();
    segs.erase(segs.begin());
    --n;

    std::sort(segs.begin(), segs.end(),
              [](const Seg& a, const Seg& b) {
                  return a.l != b.l ? a.l < b.l : a.r < b.r;
              });

    std::vector<int> back(n + 1);
    Seg backs;
    backs.l = 0, backs.r = 1e9;
    back[0] = backs.len();
    for (int i = 1; i <= n; ++i) {
        auto seg = segs[n - i];
        backs.l = std::max(backs.l, seg.l);
        backs.r = std::min(backs.r, seg.r);
        back[i] = backs.len();
    }

    int ans = 0;
    Seg fseg = base;
    for (int i = 0; i < n; ++i) {
        int f = fseg.len();
        int b = back[n - i];
        ans = std::max(ans, f + b);

        fseg.l = std::max(fseg.l, segs[i].l);
        fseg.r = std::min(fseg.r, segs[i].r);
    }

    fseg = base;
    fseg.l = std::max(fseg.l, segs.back().l);
    fseg.r = std::min(fseg.r, segs.back().r);

    for (int i = 0; i < n - 1; ++i) {
        auto seg = segs[i];
        ans = std::max(ans, seg.len() + fseg.len());
    }

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


Measured memory_bytes: 1408