#include <bits/stdc++.h>
using namespace std;
#ifndef ONLINE_JUDGE
	#include <boost/multiprecision/cpp_int.hpp>
	#include <boost/multiprecision/cpp_dec_float.hpp>
	using bll = boost::multiprecision::cpp_int;
	using bdouble = boost::multiprecision::cpp_dec_float_100;
#endif
#ifdef LOCAL_DEV
	void debug_impl() { std::cerr << std::endl; }
	template<typename Head, typename... Tail> void debug_impl(Head head, Tail... tail) { std::cerr << " " << head << (sizeof...(tail) ? "," : ""); debug_impl(tail...); }
	#define debug(...) std::cerr << std::boolalpha << "(" << #__VA_ARGS__ << ") ="; debug_impl(__VA_ARGS__); std::cerr << std::noboolalpha;
#else
	#define debug(...)
#endif
#ifdef LOCAL_TEST
	#define BOOST_STACKTRACE_USE_ADDR2LINE
	#define BOOST_STACKTRACE_ADDR2LINE_LOCATION /usr/local/opt/binutils/bin/addr2line
	#define _GNU_SOURCE
	#include <boost/stacktrace.hpp>
	template<typename T> class dvector : public std::vector<T> {
	public:
		dvector() : std::vector<T>() {}
		explicit dvector(size_t n, const T& value = T()) : std::vector<T>(n, value) {}
		dvector(const std::vector<T>& v) : std::vector<T>(v) {}
		dvector(const std::initializer_list<T> il) : std::vector<T>(il) {}
		dvector(const typename std::vector<T>::iterator first, const typename std::vector<T>::iterator last) : std::vector<T>(first, last) {}
		dvector(const std::string::iterator first, const std::string::iterator last) : std::vector<T>(first, last) {}
		T& operator[](size_t n) {
			try { return this->at(n); } catch (const std::exception& e) {
				std::cerr << boost::stacktrace::stacktrace() << std::endl; return this->at(n);
			}
		}
		const T& operator[](size_t n) const {
			try { return this->at(n); } catch (const std::exception& e) {
				std::cerr << boost::stacktrace::stacktrace() << std::endl; return this->at(n);
			}
		}
	};
	class dbool {
	private:
		bool boolvalue;
	public:
		dbool() : boolvalue(false) {}
		dbool(bool b) : boolvalue(b) {}
		dbool(const dbool &b) : boolvalue(b.boolvalue) {}
		operator bool&() { return boolvalue; }
		operator const bool&() const { return boolvalue; }
	};
	template<typename T> std::ostream& operator<<(std::ostream& s, const dvector<T>& v) {
		for (int i = 0, len = v.size(); i < len; ++i){ s << v[i]; if (i < len - 1) s << "\t"; } return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const dvector< dvector<T> >& vv) {
		for (int i = 0, len = vv.size(); i < len; ++i){ s << vv[i] << std::endl; } return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::set<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}" << std::endl; return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::multiset<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}" << std::endl; return s; }
	template<typename T1, typename T2> std::ostream& operator<<(std::ostream& s, const std::map<T1, T2>& m) {
		s << "{" << std::endl; for (auto itr = m.begin(); itr != m.end(); ++itr){ s << "\t" << (*itr).first << " : " << (*itr).second << std::endl; } s << "}" << std::endl; return s; }
	template<typename T1, typename T2> std::ostream& operator<<(std::ostream& s, const std::pair<T1, T2>& p) { 
		return s << "(" << p.first << ", " << p.second << ")"; }
	#define vector dvector
	#define bool dbool
#endif
//#define int long long
using ll = long long;
//constexpr int INF = 1e9;//INT_MAX=(1<<31)-1=2147483647
constexpr ll INF = (ll)1e18;//(1LL<<63)-1=9223372036854775807
constexpr ll MOD = (ll)1e9 + 7;
constexpr double EPS = 1e-9;
constexpr int dx[4]={1,0,-1,0};
constexpr int dy[4]={0,1,0,-1};
#define p(var) std::cout<<var<<std::endl
#define rep(i, n)   for(ll i=0, i##_length=(n); i< i##_length; ++i)
#define repeq(i, n) for(ll i=1, i##_length=(n); i<=i##_length; ++i)
#define all(v) (v).begin(), (v).end()
#define uniq(v) (v).erase(unique((v).begin(), (v).end()), (v).end());
template<typename T> inline void pv(vector<T> &v) { for(ll i=0, N=v.size(); i<N; i++) std::cout << v[i] << " \n"[i==N-1]; }
template<typename T> inline T gcd(T a, T b) { return b ? gcd(b,a%b) : a; }
template<typename T> inline T lcm(T a, T b) { return a / gcd(a,  b) * b; }
template<typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template<typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

/*-----8<-----template-----8<-----*/

/*-----8<-----library-----8<-----*/

constexpr ll N_MAX = 100000;
constexpr ll R_I_MAX = 1000000000;

ll N;
vector<ll> L;
vector<ll> R;


ll f(vector<pair<ll,ll>> &mondai){
	vector<ll> maxv(N,0),minv(N,0),rmaxv(N,0),rminv(N,0);
	ll maxval=0,minval=INF;
	rep(i,N){
		chmax(maxval,mondai[i].first);
		chmin(minval,mondai[i].second);
		maxv[i]=maxval;
		minv[i]=minval;
	}
	maxval=0,minval=INF;
	rep(j,N){
		ll i=N-1-j;
		chmax(maxval,mondai[i].first);
		chmin(minval,mondai[i].second);
		rmaxv[i]=maxval;
		rminv[i]=minval;
	}
	debug(maxv);	
	debug(minv);
	debug(rmaxv);
	debug(rminv);

	ll ans = 0;
	rep(i,N-1){//i 1問目の問題の個数　
		ll t1=max(0LL, minv[i]-maxv[i]+1);
		ll t2=max(0LL, rminv[i+1]-rmaxv[i+1]+1);
		debug(t1,t2);
		chmax(ans,t1+t2);
	}

	return ans;
}



void solve() {
	vector<ll> anslist;
  	scanf("%lld", &N);
	L.assign(N,0),R.assign(N,0);
	rep(i, N) scanf("%lld%lld", &L[i], &R[i]);

	vector<pair<ll,ll>> mondai(N);
	rep(i,N){
		mondai[i].first=L[i];
		mondai[i].second=R[i];
	}
	sort(all(mondai));
	ll ans1=f(mondai);
	anslist.push_back(ans1);

	sort(mondai.begin(), mondai.end(), [](const pair<ll,ll> &x, const pair<ll,ll> &y) {
		if(x.second != y.second)return x.second > y.second;
		return x.first < y.first;
	});
	debug(mondai);
	ll ans2=f(mondai);
	anslist.push_back(ans2);

	/////
	debug("-------------------");
	ll t=0;
	vector<pair<ll,ll>> lenv;
	rep(i,N){
		lenv.push_back({i, R[i]-L[i]+1});
	}
	sort(lenv.begin(), lenv.end(), [](const pair<ll,ll> &x, const pair<ll,ll> &y) {
		if(x.second != y.second)return x.second > y.second;
		return x.first < y.first;
	});
	debug(lenv);
	ll lmax=0,rmin=INF;
	rep(i,N){
		if(lenv[0].first==i)continue;
		chmax(lmax,L[i]);
		chmin(rmin,R[i]);
	}
	t=max(0LL,(rmin-lmax+1));
	anslist.push_back(lenv[0].second+t);


	sort(lenv.begin(), lenv.end(), [](const pair<ll,ll> &x, const pair<ll,ll> &y) {
		if(x.second != y.second)return x.second > y.second;
		return x.first > y.first;
	});
	debug(lenv);
	lmax=0,rmin=INF;
	rep(i,N){
		if(lenv[0].first==i)continue;
		chmax(lmax,L[i]);
		chmin(rmin,R[i]);
	}
	t=max(0LL,(rmin-lmax+1));
	anslist.push_back(lenv[0].second+t);

	debug(anslist);
	/////
	ll ans=*max_element(all(anslist));
	printf("%lld\n", ans);
}

signed main() {
	solve();
	return 0;
}


Measured memory_bytes: 6528