//#define NDEBUG
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <vector>

namespace n91 {

using i8 = std::int_fast8_t;
using i32 = std::int_fast32_t;
using i64 = std::int_fast64_t;
using u8 = std::uint_fast8_t;
using u32 = std::uint_fast32_t;
using u64 = std::uint_fast64_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

struct rep {
  struct itr {
    usize i;
    constexpr itr(const usize i) noexcept : i(i) {}
    void operator++() noexcept { ++i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  const itr f, l;
  constexpr rep(const usize f, const usize l) noexcept
      : f(std::min(f, l)), l(l) {}
  constexpr auto begin() const noexcept { return f; }
  constexpr auto end() const noexcept { return l; }
};
struct revrep {
  struct itr {
    usize i;
    constexpr itr(const usize i) noexcept : i(i) {}
    void operator++() noexcept { --i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  const itr f, l;
  constexpr revrep(const usize f, const usize l) noexcept
      : f(l - 1), l(std::min(f, l) - 1) {}
  constexpr auto begin() const noexcept { return f; }
  constexpr auto end() const noexcept { return l; }
};
template <class T> auto md_vec(const usize n, const T &value) {
  return std::vector<T>(n, value);
}
template <class... Args> auto md_vec(const usize n, Args... args) {
  return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
}
template <class T> constexpr T difference(const T &a, const T &b) noexcept {
  return a < b ? b - a : a - b;
}
template <class T> void chmin(T &a, const T &b) noexcept {
  if (b < a)
    a = b;
}
template <class T> void chmax(T &a, const T &b) noexcept {
  if (a < b)
    a = b;
}
template <class T> T scan() {
  T ret;
  std::cin >> ret;
  return ret;
}

} // namespace n91
#include <utility>
#include <vector>

namespace n91 {

template <class T>
std::vector<std::pair<T, std::size_t>>
run_length_encoding(const std::vector<T> &a) {
  if (a.empty()) {
    return std::vector<std::pair<T, std::size_t>>();
  }
  std::vector<std::pair<T, std::size_t>> ret;
  ret.reserve(a.size());
  ret.emplace_back(a.front(), static_cast<std::size_t>(0));
  for (const T &e : a) {
    if (e != ret.back().first) {
      ret.emplace_back(e, static_cast<std::size_t>(0));
    }
    ++ret.back().second;
  }
  ret.shrink_to_fit();
  return std::move(ret);
}

} // namespace n91

#include <algorithm>
#include <iostream>
#include <numeric>
#include <utility>

namespace n91 {

void main_() {
  constexpr u32 Inf = 1000000001;
  /*
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  //*/
  usize n = scan<usize>();
  struct it_t {
    u32 l, r;

    u32 len() const {
      if (l <= r) {
        return r - l + 1;
      } else {
        return 0;
      }
    }

    it_t operator+(const it_t &x) const {
      return it_t({std::max(l, x.l), std::min(r, x.r)});
    }
  };
  std::vector<it_t> it(n);
  u32 ans = 0;
  for (auto &e : it) {
    std::cin >> e.l >> e.r;
  }
  {
    std::vector<it_t> suf(n), pre(n);
    pre.front() = {0, Inf};
    for (const usize i : rep(0, n - 1)) {
      pre[i + 1] = pre[i] + it[i];
    }
    suf.back() = {0, Inf};
    for (const usize i : revrep(1, n)) {
      suf[i - 1] = suf[i] + it[i];
    }
    for (const usize i : rep(0, n)) {
      chmax(ans, it[i].len() + (pre[i] + suf[i]).len());
    }
  }
  std::sort(it.begin(), it.end(), [&](auto &x, auto &y) {
    if (x.r != y.r) {
      return x.r < y.r;
    } else {
      return x.l > y.l;
    }
  });
  {
    u32 lmax = 0;
    std::vector<it_t> nex;
    for (const usize i : rep(0, n)) {
      if (lmax < it[i].l) {
        nex.push_back(it[i]);
      }
      chmax(lmax, it[i].l);
    }
    it = std::move(nex);
    n = it.size();
  }
  {
    std::vector<it_t> suf(n), pre(n);
    pre.front() = {0, Inf};
    for (const usize i : rep(0, n - 1)) {
      pre[i + 1] = pre[i] + it[i];
    }
    suf.back() = it.back();
    for (const usize i : revrep(0, n - 1)) {
      suf[i] = suf[i + 1] + it[i];
    }
    for (const usize i : rep(1, n)) {
      chmax(ans, pre[i].len() + suf[i].len());
    }
  }
  std::cout << ans << std::endl;
}

} // namespace n91

int main() {
  n91::main_();
  return 0;
}


Measured memory_bytes: 5448