#include <bits/stdc++.h>
#include <unistd.h>
 
using namespace std;
 
#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}
 
 
typedef long long ll;
#define int ll
 
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const ll MOD = 1000000007;
//const ll MOD = 998244353;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx_ori[4] = { -1,0, 1,0 }, dy_ori[4] = { 0,1,0,-1 };
int dx[4] = {0, 0, 0, 0}, dy[4] = {0, 0, 0, 0};
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
// #define mp make_pair
//#define endl '\n'


const int MAXN = 100010;

vl fact(MAXN);
vl rfact(MAXN);

ll mod_pow(ll x, ll p, ll M = MOD) {
  ll a = 1;
  while (p) {
    if (p % 2)
      a = a*x%M;
    x = x*x%M;
    p /= 2;
  }
  return a;
}

ll mod_inverse(ll a, ll M = MOD) {
  return mod_pow(a, M - 2, M);
}

void set_fact(ll n, ll M = MOD) {
  fact[0] = fact[1] = rfact[0] = rfact[1] = 1;
  for (ll i = 2; i <= n; i++) {
    fact[i] = i * fact[i - 1] % M;
    // rfact[i] = mod_inverse(fact[i], M);
  }
}

//http://drken1215.hatenablog.com/entry/2018/06/08/210000
//nが大きくfactが計算できないときのほかの計算方法について書いてある
ll nCr(ll n, ll r, ll M = MOD) {
  if (r > n) return 0;
  assert(fact[2] == 2);
  ll ret = fact[n];
  if (rfact[r] == 0) {
    rfact[r] = mod_inverse(fact[r], M);
  }
  ret = (ret*rfact[r]) % M;
  if (rfact[n - r] == 0) {
    rfact[n - r] = mod_inverse(fact[n - r], M);
  }
  ret = (ret*rfact[n - r]) % M;
  return ret;
}

pll merge(pll a, pll b) {
  if (a.first == -1 or b.first == -1) return pll(-1, -1);
  if (a.first > b.first) swap(a, b);
  pll c(b.first, min(a.second, b.second));
  if (c.first >= c.second) c = pll(-1, -1);
  return c;
}

ll solve(int n, vector<pll> lr) {
  ll ans = 0;
  vector<pll> sum(n), rsum(n);
  sum[0] = lr[0];
  rep (i, n - 1) {
    sum[i + 1] = merge(sum[i], lr[i + 1]);
  }
  rsum[n - 1] = lr[n - 1];
  rrep (i, n - 1) {
    rsum[i] = merge(rsum[i + 1], lr[i]);
  }

  rep (i, n) {
    if (i == 0 or i == n - 1) continue;
    ll add = lr[i].second - lr[i].first;
    pll nokori = merge(sum[i - 1], rsum[i + 1]);
    add += nokori.second - nokori.first;
    chmax(ans, add);
  }


  
  //DEBUG_VEC(lr);
  //DEBUG_VEC(sum);
  //DEBUG_VEC(rsum);
  
  rep (i, n - 1) {
    chmax(ans, sum[i].second - sum[i].first + rsum[i + 1].second - rsum[i + 1].first);
  }
  return ans;
}

bool cmp(pll a, pll b) {
  if (a.second != b.second) return a.second < b.second;
  else a < b;
}

signed main() {
  fio();

  int n;
  cin >> n;
  vi l(n), r(n);
  vector<pll> lr;
  rep (i, n) {
    cin >> l[i] >> r[i];
    r[i]++;
    lr.push_back(pll(l[i], r[i]));
  }
  sort(all(lr));
  ll ans = solve(n, lr);
  sort(all(lr), cmp);
  ll ans2 = solve(n, lr);
  DEBUG(pll(ans, ans2));
  chmax(ans, ans2);
  cout << ans << endl;
}


Measured memory_bytes: 9840