#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using PII = pair<ll, ll>;
#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
template<typename T> void chmin(T &a, const T &b) { a = min(a, b); }
template<typename T> void chmax(T &a, const T &b) { a = max(a, b); }
struct FastIO {FastIO() { cin.tie(0); ios::sync_with_stdio(0); }}fastiofastio;
#ifdef DEBUG_ 
#include "../program_contest_library/memo/dump.hpp"
#else
#define dump(...)
#endif
const ll INF = 1LL<<60;


template <typename Monoid>
struct lazysegtree {
    using T = typename Monoid::T;
    using E = typename Monoid::E;
    int n, height;
    vector<T> dat;
    vector<E> lazy;

    lazysegtree() {}
    lazysegtree(int n_) {
        n = 1, height = 0;
        while(n < n_) { n *= 2; height++; }
        dat.assign(n*2, Monoid::dt());
        lazy.assign(n*2, Monoid::de());
    }
    void build(vector<T> v) {
        REP(i, v.size()) dat[i+n] = v[i];
        for(int i=n-1; i>0; --i) dat[i] = Monoid::f(dat[i*2], dat[i*2+1]);
    }

    inline T reflect(int k) { return lazy[k]==Monoid::de()?dat[k]:Monoid::g(dat[k], lazy[k]); }
    inline void eval(int k) {
        if(lazy[k] == Monoid::de()) return;
        lazy[2*k]   = Monoid::h(lazy[k*2],   lazy[k]);
        lazy[2*k+1] = Monoid::h(lazy[k*2+1], lazy[k]);
        dat[k] = reflect(k);
        lazy[k] = Monoid::de();
    }
    inline void thrust(int k) { for(int i=height;i;--i) eval(k>>i); }
    inline void recalc(int k) { while(k>>=1) dat[k] = Monoid::f(reflect(k*2), reflect(k*2+1)); }

    void update(int a, int b, E x) {
        thrust(a+=n);
        thrust(b+=n-1);
        for(int l=a, r=b+1; l<r; l>>=1,r>>=1) {
            if(l&1) lazy[l] = Monoid::h(lazy[l], x), ++l;
            if(r&1) --r, lazy[r] = Monoid::h(lazy[r], x);
        }
        recalc(a);
        recalc(b);
    }
    T query(int a, int b) {
        thrust(a+=n);
        thrust(b+=n-1);
        T vl=Monoid::dt(), vr=Monoid::dt();
        for(int l=a, r=b+1; l<r; l>>=1,r>>=1) {
            if(l&1) vl=Monoid::f(vl, reflect(l++));
            if(r&1) vr=Monoid::f(reflect(--r), vr);
        }
        return Monoid::f(vl, vr);
    }

    friend ostream &operator <<(ostream& out,const lazysegtree<Monoid>& seg) {
        out << "---------------------" << endl;
        int cnt = 1;
        for(int i=1; i<=seg.n; i*=2) {
            REP(j, i) {
                out << "(" << seg.dat[cnt] << "," << seg.lazy[cnt] << ") ";
                cnt++;
            }
            out << endl;
        }
        out << "---------------------" << endl;
        return out;
    }
};

struct node {
    ll sum, max, min, len;
    node() : sum(0), max(-INF), min(INF), len(0) {}
    node(ll a, ll b, ll c, ll d) : sum(a), max(b), min(c), len(d) {}
};
struct linear_exp {
    using T = node;
    using E = PII;
    static T dt() { return node(); }
    static constexpr E de() { return PII(1, 0); }
    static T f(const T &a, const T &b) {
        node ret;
        ret.sum = a.sum + b.sum;
        ret.min = min(a.min, b.min);
        ret.max = max(a.max, b.max);
        ret.len = a.len + b.len;
        return ret;
    }
    static T g(const T &a, const E &b) {
        node ret;
        ret.sum = b.first*a.sum+b.second*a.len;
        ret.min = b.first*a.min+b.second;
        ret.max = b.first*a.max+b.second;
        ret.len = a.len;
        return ret;
    }
    static E h(const E &a, const E &b) {
        return PII(b.first*a.first, b.first*a.second+b.second);
    }
};

int main(void) {
    ll n;
    cin >> n;
    vector<PII> vp(n);
    REP(i, n) cin >> vp[i].first >> vp[i].second;
    sort(ALL(vp));
    vector<ll> l(n), r(n);
    REP(i, n) l[i] = vp[i].first, r[i] = vp[i].second;

    ll mi = INF, idx = -1;
    REP(i, n) {
        if(mi > r[i]) {
            mi = r[i];
            idx = i;
        }
    }

    lazysegtree<linear_exp> seg(n);
    vector<node> init(n);
    REP(i, n) init[i] = node(r[i], r[i], r[i], 1);
    seg.build(init);

    ll ans = 0;
    REP(i, n) chmax(ans, r[i]-l[i]+1);
    REP(j, n-1) {
        ll tmp = 2 - l[j] - l[n-1];

        // [i,j] に mi を含む
        // [0,j] [j+1,n-1] について r のminを取る
        ll v1 = seg.query(0, j+1).min + seg.query(j+1, n).min;
        chmax(ans, tmp + v1);

        // [i,j] に mi を含まない
        // mi + [0,j] の r の max
        ll v2 = seg.query(0, j+1).max + mi;
        chmax(ans, tmp + v2);
    }
    cout << ans << endl;

    // vector<ll> ord(n);
    // iota(ALL(ord), 0);
    // sort(ALL(ord), [&](ll a, ll b){
    //     return l[a] > l[b];
    // });

    // dump(l);
    // dump(r);
    // dump(ord);

    // ll ans = 0;
    // REP(i, n) chmax(ans, r[i]-l[i]+1);
    // priority_queue<ll, vector<ll>, greater<ll>> que;
    // set<ll> rest;
    // REP(i, n) rest.insert(r[i]);
    // REP(i, n-1) {
    //     ll j = ord[i];
    //     que.push(r[j]); rest.erase(r[j]);
    //     dump(que);
    //     dump(rest);
    //     ll r2 = que.top(), l2 = l[ord[0]], r1 = *rest.begin(), l1 = l[ord[i+1]];
    //     dump(r2, l2, r1, l1);
    //     chmax(ans, max(0LL, r2-l2+1) + max(0LL, r1-l1+1));
    // }
    // cout << ans << endl;

    // ll ans = 0, ma = 0;
    // set<PII> interval, rest;
    // priority_queue<ll> que;
    // REP(i, n) rest.insert({-l[i], i});
    // REP(i, n) {
    //     interval.insert({-l[i], i});
    //     rest.erase({-l[i], i});
    //     ma = -rest.begin()->first;

    //     // queの再計算
    //     // -(l2 + max(next(l2), ma)) のmaxを求めたい

    //     // tailの計算
    //     ll l2 = -interval.rbegin()->first, l1 = ma;
    //     ll tail = -l2-l1;

    //     chmax(ans, r[i]+r[0]+2+max(que.top(), tail));
    // }

    return 0;
}

Measured memory_bytes: 21888