#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9;
const ll LINF = 1e18;
inline ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }
inline ll lcm(ll a, ll b) { return a / gcd(a, b)*b; }
template<class S,class T> ostream& operator << (ostream& out,const pair<S,T>& o){ out << "(" << o.first << "," << o.second << ")"; return out; }
template<class T> ostream& operator << (ostream& out,const vector<T>& V){ for(int i = 0; i < V.size(); i++){ out << V[i]; if(i!=V.size()-1) out << " ";} return out; }
template<class T> ostream& operator << (ostream& out,const vector<vector<T> >& Mat){ for(int i = 0; i < Mat.size(); i++) { if(i != 0) out << endl; out << Mat[i];} return out; }
template<class S,class T> ostream& operator << (ostream& out,const map<S,T>& mp){ out << "{ "; for(auto it = mp.begin(); it != mp.end(); it++){ out << it->first << ":" << it->second; if(mp.size()-1 != distance(mp.begin(),it)) out << ", "; } out << " }"; return out; }
template<typename T>vector<T> make_v(size_t a){return vector<T>(a);}
template<typename T,typename... Ts>auto make_v(size_t a,Ts... ts){return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));}
template<typename T,typename V> typename enable_if<is_class<T>::value==0>::type fill_v(T &t,const V &v){t=v;}
template<typename T,typename V> typename enable_if<is_class<T>::value!=0>::type fill_v(T &t,const V &v){for(auto &e:t) fill_v(e,v);}
/*
 <url:https://atcoder.jp/contests/agc040/tasks/agc040_b>
 問題文============================================================
 B - Two Contests 
 =================================================================
 解説=============================================================
 ================================================================
 */

template<class Type>
Type solve(Type res = Type()){
    int N; cin >> N;
    vector<ll> L(N),R(N);
    for(int i = 0; i < N;i++) cin >> L[i] >> R[i];
    vector<pll> RL(N);
    for(int i = 0; i < N;i++){
        RL[i] = make_pair(R[i],L[i]);
    }
    sort(RL.begin(),RL.end());
    vector<ll> get_cnt(N);
    vector<pll> Lsec(N),Rsec(N);

    {
        ll lpos = 1,rpos = 1e9;
        for(int i = N-1; i >= 0; i--){
            ll l,r; tie(r,l) = RL[i];

            lpos = max(lpos,l);
            rpos = min(rpos,r);

            Rsec[i] = make_pair(lpos,rpos);

            get_cnt[i] = max(0LL,rpos-lpos+1);
        }
    }
    // cout << get_cnt << endl;
    {
        ll lpos = 1,rpos = 1e9;
        for(int i = 0; i < N-1; i++){
            ll l,r; tie(r,l) = RL[i];
            lpos = max(lpos,l);
            rpos = min(rpos,r);

            Lsec[i] = make_pair(lpos,rpos);

            res = max(res,get_cnt[i+1]+max(0LL,rpos-lpos+1));
        }
    }

    {
        for(int i = 0; i < N;i++){
            pll ls = {1,1e9},rs = {1,1e9};

            if(i!=0) ls = Lsec[i-1];
            if(i!=N-1) rs = Rsec[i+1];

            ll v1 = max(0LL,RL[i].first - RL[i].second + 1);
            ll v2 = max(0LL,min(ls.second,rs.second) - max(ls.first,rs.first) + 1);

            res = max(res,v1+v2);
        }
    }

    return res;
}
int main(void) {
    cin.tie(0); ios::sync_with_stdio(false);
    //solve<ll>(0);
    cout << fixed << setprecision(12) << solve<ll>() << endl;
    return 0;
}

Measured memory_bytes: 10328