#ifndef DEBUG
#  define NDEBUG
#endif
#include <iostream>
#include <algorithm>
#include <string>
#include <iterator>
#include <utility>
#include <type_traits>
#include <limits>
#include <cassert>
#include <numeric>
#include <vector>

using namespace std;

// template {{{
// misc {{{
using Z = long long;
[[maybe_unused]]
constexpr Z INF = numeric_limits<Z>::max() / 3;
// }}}

// debug {{{
template <class T>
using enable_if_sequence_t = enable_if_t<
  is_same<
    typename iterator_traits<
      typename remove_cv_t<remove_reference_t<T>>::iterator
    >::iterator_category,
    random_access_iterator_tag>{}>;
#ifdef NDEBUG
# define dump(x)
# define debug if (0)
template <class T>
inline T&& ix(T&& value) { return value; }
template <class T, class Index, class... Indices, class = enable_if_sequence_t<T>>
inline auto&& ix(T&& container, Index index, Indices... indices) {
  return ix(container[index], indices...);
}
#else
# define dump(x) do { \
    cerr << "\e[33m[dump: " << __LINE__ << "] " << (#x) << " = " << x << "\e[0m" << endl; \
  } while (0);
# define debug
template <class T>
inline auto&& ix_impl([[maybe_unused]] int line, [[maybe_unused]] const char* code, T&& value) {
  return value;
}
template <class T, class Index, class... Indices, class = enable_if_sequence_t<T>>
inline auto&& ix_impl(int line, const char* code, T&& container, Index index, Indices... indices) {
  if (index < 0) {
    cerr << "\e[31mix: negative index at line " << line << ", ix(" << code << ")\e[0m" << endl;
    exit(1);
  }
  int size = container.size();
  if (index >= size) {
    cerr << "\e[31mix: index out of range at line " << line << ", ix(" << code << ")\n"
      << "index = " << index << " whereas size = " << size << "\e[0m" << endl;
    exit(1);
  }
  return ix_impl(line, code, container[index], indices...);
}
#define ix(...) ix_impl(__LINE__, #__VA_ARGS__, __VA_ARGS__)
#endif
// }}}

// IO {{{
template <class T, class U>
ostream& operator<< (ostream& os, pair<T, U> p) {
  os << '(' << p.first << ", " << p.second << ')';
  return os;
}
template <class T, class U>
istream& operator>> (istream& is, pair<T, U>& p) {
  is >> p.first >> p.second;
  return is;
}
template <class T>
false_type is_container_impl(...);
template <class T, class = typename T::iterator>
true_type is_container_impl(T);
template <class T>
struct is_container : decltype(is_container_impl<T>(declval<T>())) {};
template <>
struct is_container <string> : std::false_type {};
template <class Container, class = enable_if_t<is_container<Container>{}>>
istream& operator>> (istream& is, Container& cont) {
  for (auto& v : cont) is >> v;
  return is;
}
template <class Container, class = enable_if_t<is_container<Container>{}>>
ostream& operator<< (ostream& os, Container const& cont) {
  bool first = true;
  constexpr char sep =
    is_container<typename Container::value_type>{} ? '\n' : ' ';
  for (auto const& v : cont) {
    if (!first) {
      os << sep;
    }
    first = false;
    os << v;
  }
  return os;
}
// }}}
// }}}


template <class T>
inline void chmin(T& x, T const& v) {
  x = min(x, v);
}
template <class T>
inline void chmax(T& x, T const& v) {
  x = max(x, v);
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  Z N;
  cin >> N;
  vector<pair<Z, Z>> problems(N);
  cin >> problems;
  for (auto&& p : problems)
    p.first--;
  auto rbound = min_element(begin(problems), end(problems),
      [] (auto p, auto q) {
        if (p.second != q.second) return p.second < q.second;
        else return p.first < q.first;
      });
  auto lbound = max_element(begin(problems), end(problems));
  if (lbound == rbound) {
    auto widest = max_element(begin(problems), end(problems),
        [] (auto p, auto q) { return p.second - p.first < q.second - q.first; });
    cout << (lbound->second - lbound->first) + (widest->second - widest->first) << endl;
    return 0;
  }
  pair<Z, Z> rb = *rbound, lb = *lbound;
  dump(rb);
  dump(lb);
  swap(*lbound, problems.back());
  problems.pop_back();
  swap(*rbound, problems.back());
  problems.pop_back();
  sort(begin(problems), end(problems));
  dump(problems)
  vector<Z> minrs(N - 1, lb.second);
  for (auto i = N - 3; i >= 0; i--)
    ix(minrs, i) = min(ix(minrs, i + 1), ix(problems, i).second);
  dump(minrs);
  Z max_fun = rb.second - rb.first + max(0ll, ix(minrs, 0) - lb.first),
    leftmost = rb.first;
  auto widest = *max_element(begin(problems), end(problems),
      [] (auto p, auto q) { return p.second - p.first < q.second - q.first; });
  chmax(max_fun, max(0ll, rb.second - lb.first) + widest.second - widest.first);
  for (auto i = 0; i < N - 2; i++) {
    chmax(leftmost, ix(problems, i).first);
    chmax(max_fun, max(0ll, rb.second - leftmost) + max(0ll, ix(minrs, i + 1) - lb.first));
  }
  cout << max_fun << endl;
}



Measured memory_bytes: 2560