#include <bits/stdc++.h>
#define ADD(a, b) a = (a + ll(b)) % mod
#define MUL(a, b) a = (a * ll(b)) % mod
#define MAX(a, b) a = max(a, b)
#define MIN(a, b) a = min(a, b)
#define rep(i, a, b) for(int i = int(a); i < int(b); i++)
#define rer(i, a, b) for(int i = int(a) - 1; i >= int(b); i--)
#define all(a) (a).begin(), (a).end()
#define sz(v) (int)(v).size()
#define pb push_back
#define sec second
#define fst first
#define debug(fmt, ...) Debug(__LINE__, ":", fmt, ##__VA_ARGS__)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<int, pi> ppi;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vl> mat;
typedef complex<double> comp;
void Debug() {cerr << '\n'; }
template<class FIRST, class... REST>void Debug(FIRST arg, REST... rest){
	cerr<<arg<<" ";Debug(rest...);}
template<class T>ostream& operator<<(ostream& out,const vector<T>& v) {
	out<<"[";if(!v.empty()){rep(i,0,sz(v)-1)out<<v[i]<<", ";out<<v.back();}out<<"]";return out;}
template<class S, class T>ostream& operator<<(ostream& out,const pair<S, T>& v){
	out<<"("<<v.first<<", "<<v.second<<")";return out;}
const int MAX_N = 500010;
const int MAX_V = 100010;
const double eps = 1e-6;
const ll mod = 1000000007;
const int inf = (1 << 30) - 1;
const ll linf = 1LL << 60;
const double PI = 3.14159265358979323846;
mt19937 rng; //use it by rng() % mod, shuffle(all(vec), rng)
///////////////////////////////////////////////////////////////////////////////////////////////////

int N;
ll L[MAX_N], R[MAX_N];

void solve() {
	cin >> N;
	ll maxl = -inf, minr = inf;
	rep(i, 0, N) {
		cin >> L[i] >> R[i];
		MAX(maxl, L[i]);
		MIN(minr, R[i]);
	}
	int at = -1;
	rep(i, 0, N) {
		if(L[i] == maxl && R[i] == minr) {
			at = i; break;
		}
	}
	if(at != -1) {
		ll ans = R[at] - L[at] + 1;
		ll tmp = -inf;
		rep(i, 0, N) {
			if(at == i) continue;
			MAX(tmp, R[i] - L[i] + 1);
		}
		ans += tmp;
		cout << ans << "\n";
	}
	else {
		int lat = -1, rat = -1;
		rep(i, 0, N) {
			if(L[i] == maxl) lat = i;
			if(R[i] == minr) rat = i;
		}
		assert(lat != -1 && rat != -1 && lat != rat);
		// debug(L[rat], R[rat], L[lat], R[lat], maxl, minr);
		vector<pl> vec;

		ll tmp = -linf;
		rep(i, 0, N) {
			if(lat == i || rat == i) continue;
			vec.pb(pl(L[i], R[i]));
			MAX(tmp, R[i] - L[i] + 1);
		}
		sort(all(vec));
		multiset<ll> L1, R1, L2, R2;
		L1.insert(-linf); R1.insert(linf);
		L2.insert(-linf); R2.insert(linf);

		rep(i, 0, sz(vec)) {
			L2.insert(vec[i].fst);
			R2.insert(vec[i].sec);
		}
		ll ans = tmp + max(min(R[lat], R[rat]) - max(L[rat], L[lat]) + 1, 0ll);
		// debug(ans);
		rep(i, 0, sz(vec) + 1) {
			ll l1 = max(L[rat], *(--L1.end()));
			ll r1 = min(R[rat], *(R1.begin()));
			ll l2 = max(L[lat], *(--L2.end()));
			ll r2 = min(R[lat], *(R2.begin()));
			MAX(ans, max(r1 - l1 + 1, 0ll) + max(r2 - l2 + 1, 0ll));
			if(i == sz(vec)) break;
			L2.erase(L2.lower_bound(vec[i].fst));
			R2.erase(R2.lower_bound(vec[i].sec));
			L1.insert(vec[i].fst);
			R1.insert(vec[i].sec);
		}
		cout << ans << "\n";
	}
}

uint32_t rd() {
	uint32_t res;
#ifdef __MINGW32__
	asm volatile("rdrand %0" :"=a"(res) ::"cc");
#else
	res = std::random_device()();
#endif
	return res;
}

int main() {
#ifndef LOCAL
	ios::sync_with_stdio(false);
    cin.tie(0);
#endif
    cout << fixed;
	cout.precision(20);
    cerr << fixed;
	cerr.precision(6);
	rng.seed(rd());
#ifdef LOCAL
	//freopen("in.txt", "wt", stdout); //for tester
	if(!freopen("in.txt", "rt", stdin)) return 1;
#endif	
	solve();
    cerr << "Time: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
	return 0;
}



Measured memory_bytes: 16112