// need
#include <iostream>
#include <algorithm>
// data structure
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <complex>
//#include <deque>
#include <valarray>
#include <unordered_map>
#include <unordered_set>
#include <array>
// etc
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <chrono>
#include <random>
#include <numeric>
#include <fstream>

// input
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
template<typename T> void MACRO_VAR_Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void MACRO_VAR_Scan(First& first, Rest& ...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); }
#define VEC_ROW(type, n, ...)std::vector<type> __VA_ARGS__;MACRO_VEC_ROW_Init(n, __VA_ARGS__); for(int w_=0; w_<n; ++w_){MACRO_VEC_ROW_Scan(w_, __VA_ARGS__);}
template<typename T> void MACRO_VEC_ROW_Init(int n, T& t) { t.resize(n); }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Init(int n, First& first, Rest& ...rest) { first.resize(n); MACRO_VEC_ROW_Init(n, rest...); }
template<typename T> void MACRO_VEC_ROW_Scan(int p, T& t) { std::cin >> t[p]; }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Scan(int p, First& first, Rest& ...rest) { std::cin >> first[p]; MACRO_VEC_ROW_Scan(p, rest...); }
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& R:c)for(auto& w:R)std::cin>>w;
// output
template<typename T>void MACRO_OUT(const T t) { std::cout << t; }
template<typename First, typename...Rest>void MACRO_OUT(const First first, const Rest...rest) { std::cout << first << " "; MACRO_OUT(rest...); }
#define OUT(...) MACRO_OUT(__VA_ARGS__);
#define FOUT(n, dist) std::cout<<std::fixed<<std::setprecision(n)<<(dist);
#define SOUT(n, c, dist) std::cout<<std::setw(n)<<std::setfill(c)<<(dist);
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define SPBR(w, n) std::cout<<(w + 1 == n ? '\n' : ' ');
#define ENDL std::cout<<std::endl;
#define FLUSH std::cout<<std::flush;
#define SHOW(dist) {std::cerr << #dist << "\t: " << (dist) << "\n";}
#define SHOWVECTOR(v) {std::cerr << #v << "\t: ";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOWVECTOR2(v) {std::cerr << #v << "\t:\n";for(const auto& xxx : v){for(const auto& yyy : xxx){std::cerr << yyy << " ";}std::cerr << "\n";}}
#define SHOWQUEUE(a) {auto tmp(a);std::cerr << #a << "\t: ";while(!tmp.empty()){std::cerr << tmp.front() << " ";tmp.pop();}std::cerr << "\n";}
#define SHOWSTACK(a) {auto tmp(a);std::cerr << #a << "\t: ";while(!tmp.empty()){std::cerr << tmp.top() << " ";tmp.pop();}std::cerr << "\n";}
// utility
#define ALL(a) (a).begin(),(a).end()
#define FOR(w, a, n) for(int w=(a);w<(n);++w)
#define RFOR(w, a, n) for(int w=(n)-1;w>=(a);--w)
#define REP(w, n) for(int w=0;w<int(n);++w)
#define RREP(w, n) for(int w=int(n)-1;w>=0;--w)
#define IN(a, x, b) (a<=x && x<b)
template<class T> inline T CHMAX(T & a, const T b) { return a = (a < b) ? b : a; }
template<class T> inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; }
// test
template<class T> using V = std::vector<T>;
template<class T> using VV = V<V<T>>;

template<typename S, typename T>
std::ostream& operator<<(std::ostream& os, std::pair<S, T> p) {
	os << "(" << p.first << ", " << p.second << ")"; return os;
}

// type/const
#define int ll
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using PAIR = std::pair<int, int>;
using PAIRLL = std::pair<ll, ll>;
constexpr int INFINT = (1 << 30) - 1;                    // 1.07x10^ 9
constexpr int INFINT_LIM = (1LL << 31) - 1;              // 2.15x10^ 9
constexpr ll INFLL = 1LL << 60;                          // 1.15x10^18
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);  // 9.22x10^18
constexpr double EPS = 1e-10;
constexpr int MOD = 1000000007;
constexpr double PI = 3.141592653589793238462643383279;
template<class T, size_t N> void FILL(T(&a)[N], const T & val) { for (auto& x : a) x = val; }
template<class ARY, size_t N, size_t M, class T> void FILL(ARY(&a)[N][M], const T & val) { for (auto& b : a) FILL(b, val); }
template<class T> void FILL(std::vector<T> & a, const T & val) { for (auto& x : a) x = val; }
template<class ARY, class T> void FILL(std::vector<std::vector<ARY>> & a, const T & val) { for (auto& b : a) FILL(b, val); }
// ------------>8------------------------------------->8------------



signed main() {
	INIT;

	VAR(int, n);
	VEC_ROW(int, n, L, R);

	int ans = 0;
	{ // 片方のコンテストを最長1つのみにする
		std::priority_queue<PAIR> mL;
		std::priority_queue<PAIR, V<PAIR>, std::greater<PAIR>> mR;

		REP(i, n) {
			mL.emplace(L[i], i);
			mR.emplace(R[i], i);
		}
		REP(i, n) {
			auto pL = mL.top();
			if (pL.second == i) {
				mL.pop();
				pL = mL.top();
			}
			auto pR = mR.top();
			if (pR.second == i) {
				mR.pop();
				pR = mR.top();
			}

			CHMAX(ans, R[i] - L[i] + 1 + std::max(0ll, pR.first - pL.first + 1));

			if (mL.size() < n) mL.emplace(L[i], i);
			if (mR.size() < n) mR.emplace(R[i], i);
		}
	}
	if (n <= 2) {
		OUT(ans)BR;
		return 0;
	}

	int L1, R1, L2, R2;
	{
		PAIR mi(INFINT, INFINT);
		int mii = -1;
		REP(i, n) {
			if (mi > PAIR(R[i], L[i])) {
				mi = PAIR(R[i], L[i]);
				mii = i;
			}
		}
		L1 = L[mii];
		R1 = R[mii];
		std::swap(L[mii], L[n - 1]); L.resize(n - 1);
		std::swap(R[mii], R[n - 1]); R.resize(n - 1);
		--n;
	}
	{
		PAIR ma(-INFINT, -INFINT);
		int mai = -1;
		REP(i, n) {
			if (ma < PAIR(L[i], R[i])) {
				ma = PAIR(L[i], R[i]);
				mai = i;
			}
		}
		L2 = L[mai];
		R2 = R[mai];
		std::swap(L[mai], L[n - 1]); L.resize(n - 1);
		std::swap(R[mai], R[n - 1]); R.resize(n - 1);
		--n;
	}

	V<int> o(n);
	std::iota(ALL(o), 0);
	std::sort(ALL(o), [&](int l, int r) {
		return PAIR(L[l], R[l]) > PAIR(L[r], R[r]);
		});

	std::priority_queue<int, V<int>, std::greater<int>> pq;
	pq.emplace(R2);
	CHMAX(ans, std::max(0ll, R1 - L[o[0]] + 1) + R2 - L2 + 1);
	int miL = L[o[0]];
	REP(i_, n) {
		int i = o[i_];

		pq.emplace(R[i]);
		if(i_ + 1 < n) CHMIN(miL, L[o[i_ + 1]]);
		CHMAX(miL, L1);
		CHMAX(ans, std::max(0ll, R1 - miL + 1) + std::max(0ll, pq.top() - L2 + 1));
	}
	OUT(ans)BR;

	return 0;
}

Measured memory_bytes: 5228