//四則演算 #pragma GCC target("avx")
//並列計算 #pragma GCC optimize("O3")
//条件分岐を減らす #pragma GCC optimize("unroll-loops")
//浮動小数点演算 #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using VI = vector<int>;
using VL = vector<ll>;
using VS = vector<string>;
template<class T> using PQ = priority_queue<T, vector<T>, greater<T>>;
#define FOR(i,a,n) for(int i=(a);i<(n);++i)
#define eFOR(i,a,n) for(int i=(a);i<=(n);++i)
#define rFOR(i,a,n) for(int i=(n)-1;i>=(a);--i)
#define erFOR(i,a,n) for(int i=(n);i>=(a);--i)
#define each(i, a) for(auto &i : a)
#define SORT(a) sort(a.begin(),a.end())
#define rSORT(a) sort(a.rbegin(),a.rend())
#define fSORT(a,f) sort(a.begin(),a.end(),f)
#define all(a) a.begin(),a.end()
#define out(y,x) ((y)<0||h<=(y)||(x)<0||w<=(x))
#define tp(a,i) get<i>(a)
#define line cout << "-----------------------------\n" 
#define ENDL(i,n) ((i) == (n) - 1 ? "\n" : " ")
#define stop system("pause")
constexpr ll INF = 1000000000;
constexpr ll LLINF = 1LL << 60;
constexpr ll mod = 1000000007;
constexpr ll MOD = 998244353;
constexpr ld eps = 1e-10;
constexpr ld pi = 3.1415926535897932;
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; }
inline void init() { cin.tie(nullptr); cout.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); }
template<class T>inline istream& operator>>(istream& is, vector<T>& v) { for (auto& a : v)is >> a; return is; }
template<class T>inline istream& operator>>(istream& is, deque<T>& v) { for (auto& a : v)is >> a; return is; }
template<class T, class U>inline istream& operator>>(istream& is, pair<T, U>& p) { is >> p.first >> p.second; return is; }
template<class T>inline vector<T> vec(size_t a) { return vector<T>(a); }
template<class T>inline vector<T> defvec(T def, size_t a) { return vector<T>(a, def); }
template<class T, class... Ts>inline auto vec(size_t a, Ts... ts) { return vector<decltype(vec<T>(ts...))>(a, vec<T>(ts...)); }
template<class T, class... Ts>inline auto defvec(T def, size_t a, Ts... ts) { return vector<decltype(defvec<T>(def, ts...))>(a, defvec<T>(def, ts...)); }
template<class T>inline void print(const T& a) { cout << a << "\n"; }
template<class T, class... Ts>inline void print(const T& a, const Ts&... ts) { cout << a << " "; print(ts...); }
template<class T>inline void print(const vector<T>& v) { for (int i = 0; i < v.size(); ++i)cout << v[i] << (i == v.size() - 1 ? "\n" : " "); }
template<class T>inline void print(const vector<vector<T>>& v) { for (auto& a : v)print(a); }
inline string reversed(const string& s) { string t = s; reverse(all(t)); return t; }

template<class T> class sparsetable {
    function<T(T, T)> fun;
    vector<vector<T>> dat;
    VI len;
    int n, log;
public:
    sparsetable(const vector<T>& a, const function<T(T, T)>& F) : n(a.size()), log(log2(n)), fun(F) {
        dat = vec<T>(log + 1, n);
        len.resize(n + 1);
        FOR(i, 0, n)dat[0][i] = a[i];
        FOR(j, 0, log)FOR(i, 0, n - (1 << j)) {
            dat[j + 1][i] = fun(dat[j][i], dat[j][i + (1 << j)]);
        }
        eFOR(i, 2, n)len[i] = len[i >> 1] + 1;
    }
    T value(int l, int r) {
        int k = len[r - l];
        return fun(dat[k][l], dat[k][r - (1 << k)]);
    }
};

int main() {
    init();

    int n; cin >> n;
    vector<pair<int, int>> lr(n); cin >> lr;
    SORT(lr);
    VI l(n), r(n);
    FOR(i, 0, n) {
        l[i] = lr[i].first - 1;
        r[i] = lr[i].second;
    }
    sparsetable<int> l_max(l, [](int a, int b) {return max(a, b); });
    sparsetable<int> r_min(r, [](int a, int b) {return min(a, b); });

    int ans = max(r[0] - l[0] + max(r_min.value(1, n) - l_max.value(1, n), 0),
        r[n - 1] - l[n - 1] + max(r_min.value(0, n - 1) - l_max.value(0, n - 1), 0));
    FOR(i, 1, n - 1) {
        chmax(ans, max(r_min.value(0, i + 1) - l_max.value(0, i + 1), 0)
            + max(r_min.value(i + 1, n) - l_max.value(i + 1, n), 0));
        chmax(ans, r[i] - l[i] + max(min(r_min.value(0, i), r_min.value(i + 1, n))
            - max(l_max.value(0, i), l_max.value(i + 1, n)), 0));
    }
    print(ans);

    return 0;
}

Measured memory_bytes: 19192