#include <algorithm>
#include <bitset>
#include <climits>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <vector>

#define MOD 1000000007
#define PI 3.14159265358979

#define rep(i, n) for (int i = 0; i < (int)(n); i++)

using namespace std;

typedef pair< int, int > pii;
typedef long long ll;

struct edge {
	int from, to, d, c;
	edge(int _from = 0, int _to = 0, int _d = 0, int _c = 0) {
		from = _from;
		to = _to;
		d = _d;
		c = _c;
	}
	bool operator<(const edge &rhs) const {
		return (d == rhs.d) ? (c < rhs.c) : (d < rhs.d);
	}
};

typedef vector< edge > edges;
typedef vector< edges > graph;
struct flow {
	int to, cap, rev, cost;
	flow(int to = 0, int cap = 0, int rev = 0, int cost = 0) : to(to), cap(cap), rev(rev), cost(cost) {}
};
typedef vector< vector< flow > > flows;

const int di[4] = {0, -1, 0, 1};
const int dj[4] = {-1, 0, 1, 0};
const int ci[5] = {0, 0, -1, 0, 1};
const int cj[5] = {0, -1, 0, 1, 0};
const ll LINF = LLONG_MAX / 2;
const int INF = INT_MAX / 2;

template < typename T >
bool chmin(T &x, const T &y) {
	if (x > y) {
		x = y;
		return true;
	}
	return false;
}
template < typename T >
bool chmax(T &x, const T &y) {
	if (x < y) {
		x = y;
		return true;
	}
	return false;
}

struct initializer {
	initializer() {
		cout << fixed << setprecision(11);
	}
};
initializer _____;

struct SegT1 {
	vector< ll > container;
	int n;
	void update(int i, ll x) {
		int ii = i + n - 1;
		container[ii] = x;
		while (ii > 0) {
			ii = (ii - 1) / 2;
			//////////////////////////////////////////
			container[ii] = min(container[2 * ii + 1], container[2 * ii + 2]);
			//////////////////////////////////////////
		}
	}
	ll get(int l, int r, int l2 = 0, int r2 = -1, int k = 0) {
		if (r2 == -1)
			r2 = n;
		///////////////////////////////////
		if (r2 <= l || r <= l2)
			return LONG_MAX / 2;
		///////////////////////////////////
		if (l <= l2 && r2 <= r)
			return container[k];
		ll vl = get(l, r, l2, (l2 + r2) / 2, 2 * k + 1);
		ll vr = get(l, r, (l2 + r2) / 2, r2, 2 * k + 2);
		///////////////////////////
		return min(vl, vr);
		///////////////////////////
	}
	////////////////new///////////////////////
	SegT1(vector< int > &A) {
		n = pow(2, (int)log2(A.size()) + 1);
		container = vector< ll >(2 * n, 0);
		for (int i = 0; i < A.size(); i++)
			update(i, A[i]);
	}
};
struct SegT2 {
	vector< ll > container;
	int n;
	void update(int i, ll x) {
		int ii = i + n - 1;
		container[ii] = x;
		while (ii > 0) {
			ii = (ii - 1) / 2;
			//////////////////////////////////////////
			container[ii] = max(container[2 * ii + 1], container[2 * ii + 2]);
			//////////////////////////////////////////
		}
	}
	ll get(int l, int r, int l2 = 0, int r2 = -1, int k = 0) {
		if (r2 == -1)
			r2 = n;
		///////////////////////////////////
		if (r2 <= l || r <= l2)
			return 0;
		///////////////////////////////////
		if (l <= l2 && r2 <= r)
			return container[k];
		ll vl = get(l, r, l2, (l2 + r2) / 2, 2 * k + 1);
		ll vr = get(l, r, (l2 + r2) / 2, r2, 2 * k + 2);
		///////////////////////////
		return max(vl, vr);
		///////////////////////////
	}
	////////////////new///////////////////////
	SegT2(vector< int > &A) {
		n = pow(2, (int)log2(A.size()) + 1);
		container = vector< ll >(2 * n, 0);
		for (int i = 0; i < A.size(); i++)
			update(i, A[i]);
	}
};

struct range {
	ll l, r;
	range(int l = 0, int r = 0) : l(l), r(r) {}
	bool operator<(const range &rhs) const {
		if (l == rhs.l)
			return r < rhs.r;
		else {
			return l < rhs.l;
		}
	}
};

int N, M, K, T, Q;
int main() {
	cin >> N;
	ll ans = 0;
	vector< range > R(N);
	rep(i, N) cin >> R[i].l >> R[i].r;
	sort(R.begin(), R.end());
	vector< int > l(N), r(N);
	rep(i, N) {
		l[i] = R[i].l;
		r[i] = R[i].r;
		chmax(ans, (ll)(r[i] - l[i] + 1));
	}
	SegT1 rmin(r);
	SegT2 lmax(l);
	ans += max(rmin.get(0, N) - lmax.get(0, N) + 1, 0LL);
	ll ansl = 0, ansr = INT_MAX / 2;
	rep(i, N - 1) {
		range tmp = R[i];
		chmax(ansl, tmp.l);
		chmin(ansr, R[i].r);
		chmax(ans, max(ansr - ansl + 1, 0LL) + max(rmin.get(i + 1, N) - lmax.get(i + 1, N) + 1, 0LL));
	}
	cout << ans << endl;
	return 0;
}

Measured memory_bytes: 6784