/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author
 */

#include <iostream>
#include <fstream>

#ifndef  _TB
#define _TB

#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = a; i < b; ++i)
#define RFOR(i, b, a) for(int i = b - 1; i >= a; --i)
#define REP(i, N) FOR(i, 0, N)
#define RREP(i, N) RFOR(i, N, 0)

#define MIN(A, B) ((A) < (B) ? (A) : (B))
#define MAX(A, B) ((A) > (B) ? (A) : (B))
#define ABS(A) ((A) < 0 ? (-(A)) : (A))
#define ALL(V) V.begin(), V.end()
#define SIZE(V) (int)V.size()
#define pb push_back
#define mp make_pair
#define EPS 1e-7
#define Pi 3.14159265358979
#define FILL(a,v) memset(a,v,sizeof(a))

using namespace std;

typedef long long Long;
typedef unsigned long long ULong;
typedef unsigned int Uint;
typedef unsigned char Uchar;
typedef vector <int> VI;
typedef pair <int, int> PII;

#define X first
#define Y second

typedef std::pair<int,int> pii; typedef long long ll; typedef unsigned long long ull; typedef unsigned int ui; typedef pair<ui,ui> puu;

template <typename T, typename U> std::istream&operator>>(std::istream&i, pair<T,U>&p) {i >> p.X >> p.Y; return i;}
template<typename T>std::istream&operator>>(std::istream&i,vector<T>&t) {for(auto&v:t){i>>v;}return i;}
template <typename T, typename U> std::ostream&operator<<(std::ostream&o, const pair<T,U>&p) {o << p.X << ' ' << p.Y; return o;}
template<typename T>std::ostream&operator<<(std::ostream&o,const vector<T>&t) {if(t.empty())o<<'\n';for(size_t i=0;i<t.size();++i){o<<t[i]<<" \n"[i == t.size()-1];}return o;}
template<typename T> using minheap = priority_queue<T, vector<T>, greater<T>>;
template<typename T> using maxheap = priority_queue<T, vector<T>, less<T>>;
template <typename T> bool in(T a, T b, T c) { return a <= b && b < c; }
ui logceil(int x) { return (ui)(8*sizeof(int)-__builtin_clz(x)); }

namespace std { template<typename T,typename U>struct hash<pair<T,U>>{hash<T>t;hash<U>u;size_t operator()(const pair<T,U>&p)const{return t(p.x)^(u(p.y)<<7);}}; }
template<typename T> T gcd(T a,T b) { if (a<b) swap(a,b); return b?gcd(b,a%b):a; }

template<typename T>class vector2:public vector<vector<T>>{public:vector2(){} vector2(size_t a,size_t b,T t=T()):vector<vector<T>>(a,vector<T>(b,t)){}};
template<typename T>class vector3:public vector<vector2<T>>{public:vector3(){} vector3(size_t a,size_t b,size_t c,T t=T()):vector<vector2<T>>(a,vector2<T>(b,c,t)){}};
template<typename T>class vector4:public vector<vector3<T>>{public:vector4(){} vector4(size_t a,size_t b,size_t c,size_t d,T t=T()):vector<vector3<T>>(a,vector3<T>(b,c,d,t)){}};
template<typename T>class vector5:public vector<vector4<T>>{public:vector5(){} vector5(size_t a,size_t b,size_t c,size_t d,size_t e,T t=T()):vector<vector4<T>>(a,vector4<T>(b,c,d,e,t)){}};

void fastIO(){ios::sync_with_stdio(false); }

#endif

typedef pair<Long, Long> pll;


pll intersect(pll a, pll b) {
    if (a.Y < b.X || b.Y < a.X)
        return {0,0};

    return {
        max(a.X, b.X),
        min(a.Y, b.Y)
    };
}


set<pll> vx;
set<pll, greater<> > vy;

void erase(pll p) {
    vx.erase(p);
    vy.erase({p.Y, p.X});
}


pll findo(pll a) {
    if (!vx.empty()) {
        auto it = vx.upper_bound({a.Y+1, 0});
        if (it != vx.end())
            return *it;
    }

    if (!vy.empty()) {
        auto it = vy.upper_bound({a.X - 1, 1e10});
        if (it != vy.end())
            return {it->second, it->first};
    }
    return {0,0};
}


Long sss(pll p) {
    if (p.X == 0)
        return 0;
    return p.Y - p.X + 1;
}

class BTwoContests {
public:
    void solve(std::istream& in, std::ostream& out) {
        fastIO();
        int n;
        in >> n;
        vector<pll> v(n);
        in >> v;

        Long ans = 0;
        Long miny = 1e12;
        Long maxx = 0;

        vx.clear();
        vy.clear();

        for(auto p: v) {
            ans = max(ans, sss(p));
            maxx = max(maxx, p.X);
            miny = min(miny, p.Y);

            vx.insert(p);
            vy.insert({p.Y, p.X});
        }

        sort(ALL(v));
        if (vx.size() <= 2) {
            out << sss(v[0]) + sss(v.back()) << endl;
            return;
        }

        // two distinct
        if (maxx > miny) {
            pll a, b;
            for(auto p: v) {
                if (p.X == maxx)
                    a = p;
                if (p.Y == miny)
                    b = p;
            }

            erase(a);
            erase(b);

            bool changed = true;

            while (changed) {
                changed = false;
                auto oa = findo(a);
                if (oa.X != 0) {
                    b = intersect(oa, b);
                    erase(oa);
                    changed = true;
                }

                auto ob = findo(b);
                if (ob.X != 0) {
                    a = intersect(a, ob);
                    erase(ob);
                    changed = true;
                }

            }

            if (sss(a) == 0 || sss(b) == 0) {
                out << ans << endl;
                return;
            }

            vector<pll> v;

            v.pb({sss(a), 0});
            v.pb({0, -sss(b)});
            for(auto p: vx) {
                v.pb({
                    sss(intersect(p, a)),
                    -sss(intersect(p, b))
                });
            }

            Long best = 0;

            sort(ALL(v));

            Long mn = -v[0].Y;
            FOR(i, 1, v.size()) {
                best = max(best, mn+v[i].X);
                mn = min(mn, -v[i].Y);
            }

            ans = max(ans, best);
            out << ans << endl;
            return;
        }

        if (vx.count({maxx, miny})) {
            out << ans + sss({maxx, miny}) << endl;
            return;
        }


        auto firstl = *vy.rbegin();
        firstl = {
            firstl.Y, firstl.X
        };

        erase(firstl);

        vector<pll> tod;
        for(auto p: vx) {
            if (intersect(p, firstl) == firstl)
                tod.pb(p);
        }

        Long mxsize = 0;

        for (auto p: tod) {
            erase(p);
            mxsize = max(mxsize, sss(p));
        }


        auto d2 = *vx.rbegin();

        erase(d2);
        for(auto p: vx) {
            mxsize = max(mxsize, sss(p));
        }

        ans = max(mxsize + sss(intersect(d2, firstl)), ans);

        while (!vx.empty()) {
            auto cand = *vx.rbegin();
            ans = max(ans, sss(d2) + sss(intersect(firstl, cand)));
            d2 = intersect(d2, cand);
            erase(cand);
        }

        ans = max(ans, sss(d2) + sss(firstl));

        out << ans << endl;

    }
};


int main() {
	BTwoContests solver;
	std::istream& in(std::cin);
	std::ostream& out(std::cout);
	solver.solve(in, out);
	return 0;
}


Measured memory_bytes: 16500