#include <bits/stdc++.h>
using namespace std;
#define Rep(i,n) for(int i=0;i<(int)(n);i++)
#define For(i,n1,n2) for(int i=(int)(n1);i<(int)(n2);i++)
#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define RREP(i,n) for(ll i=((ll)(n)-1);i>=0;i--)
#define FOR(i,n1,n2) for(ll i=(ll)(n1);i<(ll)(n2);i++)
#define RFOR(i,n1,n2) for(ll i=((ll)(n1)-1);i>=(ll)(n2);i--)
#define all(a)  (a).begin(),(a).end()
#define SORT(a) sort((a).begin(),(a).end())
#define oorret 0
#define oor(x) [&](){try{x;} catch(const out_of_range& oor){return oorret;} return x;}()
#define IOS cin.tie(0),ios::sync_with_stdio(false)
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
template<typename T1, typename T2> inline bool chmin(T1& a, T2 b) { if (a > b) { a = b; return 1; }return 0; }
template<typename T1, typename T2> inline bool chmax(T1& a, T2 b) { if (a < b) { a = b; return 1; }return 0; }
template<class Type>struct is_vector : std::false_type {};
template<class ValueType, class Alloc>struct is_vector<std::vector<ValueType, Alloc>> : std::true_type {};
template <typename T> inline ostream& operator << (ostream& out, const vector<T>& v) {
	if (v.empty())return out;
	constexpr bool is_vector_v = is_vector<T>::value;
	if (is_vector_v)for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? "\n" : "");
	else for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? " " : "");
	return out;
}
inline void put() {}
template<class T> inline void put(const T& first) { std::cout << first << "\n"; }
template<class T, class... N> inline void put(const T& first, const N& ... rest) { std::cout << first << " "; put(rest...); }
inline void putn() {}
template<class T, class... N> inline void putn(const T& first, const N& ... rest) { std::cout << first << "\n"; putn(rest...); }


int main() {
	int n;
	cin >> n;
	vector<int> l(n), r(n);
	vector<P> p(n),p2(n),p3(n);
	REP(i, n) {
		cin >> l[i] >> r[i];
		p[i].first = l[i];
		p[i].second = r[i];
		p2[i].first = r[i];
		p2[i].second = l[i];
		p3[i].first = l[i] - r[i];
		p3[i].second = i;
	}
	sort(all(p));
	ll res = 0;
	vector<int> t1(n - 1), t2(n - 1);
	int maxl=0, minr=1e9+1;
	
	REP(i, n - 1) {
		chmax(maxl, p[i].first);
		chmin(minr, p[i].second);
		t1[i] = max(0, minr - maxl + 1);
	}

	maxl = 0, minr = 1e9 + 1;
	RFOR(i, n, 1) {
		chmax(maxl, p[i].first);
		chmin(minr, p[i].second);
		t2[i - 1] = max(0, minr - maxl + 1);
	}
	REP(i, n - 1) {
		chmax(res, t1[i] + t2[i]);
	}

	sort(all(p2));
	//vector<int> t1(n - 1), t2(n - 1);
	maxl = 0, minr = 1e9 + 1;

	REP(i, n - 1) {
		chmax(maxl, p2[i].second);
		chmin(minr, p2[i].first);
		t1[i] = max(0, minr - maxl + 1);
	}

	maxl = 0, minr = 1e9 + 1;
	RFOR(i, n, 1) {
		chmax(maxl, p2[i].second);
		chmin(minr, p2[i].first);
		t2[i - 1] = max(0, minr - maxl + 1);
	}
	REP(i, n - 1) {
		chmax(res, t1[i] + t2[i]);
	}

	sort(all(p3));
	maxl = 0, minr = 1e9 + 1;

	REP(i, n - 1) {
		int index = p3[i].second;
		chmax(maxl, l[index]);
		chmin(minr, r[index]);
		t1[i] = max(0, minr - maxl + 1);
	}
	maxl = 0, minr = 1e9 + 1;

	RFOR(i, n, 1) {
		int index = p3[i].second;
		chmax(maxl, l[index]);
		chmin(minr, r[index]);
		t2[i - 1] = max(0, minr - maxl + 1);
	}
	REP(i, n - 1) {
		chmax(res, t1[i] + t2[i]);
	}


	put(res);
	return 0;
}


Measured memory_bytes: 6528