// includes
#include <bits/stdc++.h>
using namespace std;

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define whole(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define bit(n) (1LL<<(n))
#define F first
#define S second
// functions
template <typename T> void unique(T& c){c.erase(std::unique(c.begin(), c.end()), 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;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << "(" << p.first << ", " << p.second << ")"; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << "(" << itr->first << ", " << itr->second << ")"; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << "(" << itr->first << ", " << itr->second << ")"; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 60;
const double EPS = 1e-10;
const ll mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io{
  fast_io(){ios_base::sync_with_stdio(false); cin.tie(nullptr); cout << fixed << setprecision(20);}
} fast_io_;


int main(int argc, char const* argv[])
{
  int n; cin >> n;
  vector<ll> l(n), r(n);
  rep(i, n)cin >> l[i] >> r[i];
  vector<int> el(n); rep(i, n)el[i] = i;
  sort(whole(el), [&](int i, int j){
    if(l[i] != l[j])return l[i] < l[j];
    if(r[i] != r[j])return r[i] < r[j];
    return i < j;
  });
  vector<int> er(n); rep(i, n)er[i] = i;
  sort(whole(er), [&](int i, int j){
    if(r[i] != r[j])return r[i] < r[j];
    if(l[i] != l[j])return l[i] > l[j];
    return i < j;
  });
  map<ll, int> mpr, mpl;
  map<ll, int> cnt;
  rep(i, n){
    if(i == er[0])continue;
    mpr[r[i]]++;
    mpl[l[i]]++;
    cnt[r[i] - l[i] + 1]++;
  }
  ll res = 0;
  chmax(res, r[er[0]] - l[er[0]] + 1 + max(0LL, mpr.begin()->first - mpl.rbegin()->first + 1));
  ll maxlen = 0;
  rep(i, n){
    if(i == er[0] || i == el.back())continue;
    chmax(maxlen, r[i] - l[i] + 1);
  }
  chmax(res, maxlen + max(0LL, r[er[0]] - l[el.back()] + 1));
  rep(i_, n){
    int i = el[i_];
    //cerr << "-----------------------" << endl;
    //cerr << i << endl;
    if(i != er[0]){
      if(mpr.find(r[i]) != mpr.end())mpr[r[i]]--;
      if(mpr[r[i]] == 0)mpr.erase(r[i]);
      if(mpl.find(l[i]) != mpl.end())mpl[l[i]]--;
      if(mpl[l[i]] == 0)mpl.erase(l[i]);
    }
    if(sz(mpr)){
      chmax(res, max(0LL, r[er[0]] - max(l[i], l[er[0]]) + 1) + max(0LL, mpr.begin()->first - mpl.rbegin()->first + 1));
      //cerr << mpl << endl;
      //cerr << mpr << endl;
      //cerr << max(0LL, r[er[0]] - l[i] + 1) + max(0LL, mpr.begin()->first - mpl.rbegin()->first + 1) << endl;
    }
    /*if(l[i] > r[er[0]]){
      cnt[r[i] - l[i] + 1]--;
      if(cnt[r[i] - l[i] + 1] == 0)cnt.erase(r[i] - l[i] + 1);
      cnt[r[er[0]] - l[er[0]] + 1]--;
      if(cnt[r[er[0]] - l[er[0]] + 1] == 0)cnt.erase(r[er[0]] - l[er[0]] + 1);
      chmax(res, cnt.rbegin()->first);
      cnt[r[i] - l[i] + 1]++;
      cnt[r[er[0]] - l[er[0]] + 1]++;
    }*/
    //cerr << "-----------------------" << endl;
  }
  rep(i, n)chmax(res, r[i] - l[i] + 1);
  bool ok = true;
  rep(i, n){
    if(!(l[i] <= l[er[0]] && r[er[0]] <= r[i]))ok = false;
  }
  if(ok){
    ll maxi = 0;
    rep(i, n)chmax(maxi, r[i] - l[i] + 1);
    chmax(res, maxi + r[er[0]] - l[er[0]] + 1);
  }
  cout << res << endl;
  return 0;
}


Measured memory_bytes: 21376