#include <bits/stdc++.h>

using namespace std;

using int64 = long long;
const int mod = 1e9 + 7;

const int64 infll = (1LL << 62) - 1;
const int inf = (1 << 30) - 1;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;


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 >
istream &operator>>(istream &is, pair< T1, T2 > &p) {
  is >> p.first >> p.second;
  return is;
}

template< typename T >
ostream &operator<<(ostream &os, const vector< T > &v) {
  for(int i = 0; i < (int) v.size(); i++) {
    os << v[i] << (i + 1 != v.size() ? " " : "");
  }
  return os;
}

template< typename T >
istream &operator>>(istream &is, vector< T > &v) {
  for(T &in : v) is >> in;
  return is;
}

template< typename T1, typename T2 >
inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

template< typename T1, typename T2 >
inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

template< typename T = int64 >
vector< T > make_v(size_t a) {
  return vector< T >(a);
}

template< typename T, typename... Ts >
auto make_v(size_t a, Ts... ts) {
  return vector< decltype(make_v< T >(ts...)) >(a, make_v< T >(ts...));
}

template< typename T, typename V >
typename enable_if< is_class< T >::value == 0 >::type fill_v(T &t, const V &v) {
  t = v;
}

template< typename T, typename V >
typename enable_if< is_class< T >::value != 0 >::type fill_v(T &t, const V &v) {
  for(auto &e : t) fill_v(e, v);
}

template< typename F >
struct FixPoint : F {
  FixPoint(F &&f) : F(forward< F >(f)) {}

  template< typename... Args >
  decltype(auto) operator()(Args &&... args) const {
    return F::operator()(*this, forward< Args >(args)...);
  }
};

template< typename F >
inline decltype(auto) MFP(F &&f) {
  return FixPoint< F >{forward< F >(f)};
}

template< typename Monoid, typename OperatorMonoid = Monoid >
struct LazySegmentTree {
  using F = function< Monoid(Monoid, Monoid) >;
  using G = function< Monoid(Monoid, OperatorMonoid) >;
  using H = function< OperatorMonoid(OperatorMonoid, OperatorMonoid) >;

  int sz, height;
  vector< Monoid > data;
  vector< OperatorMonoid > lazy;
  const F f;
  const G g;
  const H h;
  const Monoid M1;
  const OperatorMonoid OM0;


  LazySegmentTree(int n, const F f, const G g, const H h,
                  const Monoid &M1, const OperatorMonoid OM0)
      : f(f), g(g), h(h), M1(M1), OM0(OM0) {
    sz = 1;
    height = 0;
    while(sz < n) sz <<= 1, height++;
    data.assign(2 * sz, M1);
    lazy.assign(2 * sz, OM0);
  }

  void set(int k, const Monoid &x) {
    data[k + sz] = x;
  }

  void build() {
    for(int k = sz - 1; k > 0; k--) {
      data[k] = f(data[2 * k + 0], data[2 * k + 1]);
    }
  }

  inline void propagate(int k) {
    if(lazy[k] != OM0) {
      lazy[2 * k + 0] = h(lazy[2 * k + 0], lazy[k]);
      lazy[2 * k + 1] = h(lazy[2 * k + 1], lazy[k]);
      data[k] = reflect(k);
      lazy[k] = OM0;
    }
  }

  inline Monoid reflect(int k) {
    return lazy[k] == OM0 ? data[k] : g(data[k], lazy[k]);
  }

  inline void recalc(int k) {
    while(k >>= 1) data[k] = f(reflect(2 * k + 0), reflect(2 * k + 1));
  }

  inline void thrust(int k) {
    for(int i = height; i > 0; i--) propagate(k >> i);
  }

  void update(int a, int b, const OperatorMonoid &x) {
    thrust(a += sz);
    thrust(b += sz - 1);
    for(int l = a, r = b + 1; l < r; l >>= 1, r >>= 1) {
      if(l & 1) lazy[l] = h(lazy[l], x), ++l;
      if(r & 1) --r, lazy[r] = h(lazy[r], x);
    }
    recalc(a);
    recalc(b);
  }

  Monoid query(int a, int b) {
    thrust(a += sz);
    thrust(b += sz - 1);
    Monoid L = M1, R = M1;
    for(int l = a, r = b + 1; l < r; l >>= 1, r >>= 1) {
      if(l & 1) L = f(L, reflect(l++));
      if(r & 1) R = f(reflect(--r), R);
    }
    return f(L, R);
  }

  Monoid operator[](const int &k) {
    return query(k, k + 1);
  }

  template< typename C >
  int find_subtree(int a, const C &check, Monoid &M, bool type) {
    while(a < sz) {
      propagate(a);
      Monoid nxt = type ? f(reflect(2 * a + type), M) : f(M, reflect(2 * a + type));
      if(check(nxt)) a = 2 * a + type;
      else M = nxt, a = 2 * a + 1 - type;
    }
    return a - sz;
  }

  template< typename C >
  int find_first(int a, const C &check) {
    Monoid L = M1;
    if(a <= 0) {
      if(check(f(L, reflect(1)))) return find_subtree(1, check, L, false);
      return -1;
    }
    thrust(a + sz);
    int b = sz;
    for(a += sz, b += sz; a < b; a >>= 1, b >>= 1) {
      if(a & 1) {
        Monoid nxt = f(L, reflect(a));
        if(check(nxt)) return find_subtree(a, check, L, false);
        L = nxt;
        ++a;
      }
    }
    return -1;
  }


  template< typename C >
  int find_last(int b, const C &check) {
    Monoid R = M1;
    if(b >= sz) {
      if(check(f(reflect(1), R))) return find_subtree(1, check, R, true);
      return -1;
    }
    thrust(b + sz - 1);
    int a = sz;
    for(b += sz; a < b; a >>= 1, b >>= 1) {
      if(b & 1) {
        Monoid nxt = f(reflect(--b), R);
        if(check(nxt)) return find_subtree(b, check, R, true);
        R = nxt;
      }
    }
    return -1;
  }
};

int main() {
  int N;
  cin >> N;
  vector< int64 > L(N), R(N);

  vector< int64 > xs;
  for(int i = 0; i < N; i++) {
    cin >> L[i] >> R[i];
    ++R[i];
    for(int j = -1; j <= 1; j++) {
      xs.emplace_back(L[i] + j);
      xs.emplace_back(R[i] + j);
    }
  }
  xs.emplace_back(0);
  xs.emplace_back(inf);
  sort(begin(xs), end(xs));
  xs.erase(unique(begin(xs), end(xs)), end(xs));

  using pi = pair< int64, int64 >;
  auto f = [](pi a, pi b) {
    if(a.second == b.second) return pi(a.first + b.first, a.second);
    if(a.second > b.second) return a;
    return b;
  };
  auto g = [](pi a, int64 b) {
    return pi(a.first, a.second + b);
  };
  auto h = [](int64 a, int64 b) {
    return a + b;
  };
  LazySegmentTree< pi, int64 > seg1(xs.size(), f, g, h, pi(0, -inf), 0);
  LazySegmentTree< pi, int64 > seg2(xs.size(), f, g, h, pi(0, -inf), 0);
  for(int i = 0; i < N; i++) {
    L[i] = lower_bound(begin(xs), end(xs), L[i]) - begin(xs);
    R[i] = lower_bound(begin(xs), end(xs), R[i]) - begin(xs);
  }
  for(int i = 1; i < xs.size(); i++) {
    seg1.set(i, pi(xs[i] - xs[i - 1], 0));
    seg2.set(i, pi(xs[i] - xs[i - 1], 0));
  }
  seg1.build();
  seg2.build();
  for(int i = 0; i < N; i++) {
    seg2.update(L[i], R[i], 1);
  }
  vector< vector< int > > ev(xs.size());
  for(int i = 0; i < N; i++) {
    ev[R[i]].emplace_back(i);
  }

  int64 ret = 0;
  int malta = N, latte = 0;
  for(int i = 0; i < xs.size(); i++) {
    for(auto &p : ev[i]) {
      seg2.update(L[p], R[p], -1);
      seg1.update(L[p], R[p], 1);
      ++latte;
      --malta;
      auto res1 = seg1.query(0, xs.size());
      if(res1.second < latte) res1.first = 0;
      auto res2 = seg2.query(0, xs.size());
      if(res2.second < malta) res2.first = 0;
      if(latte && malta) chmax(ret, res1.first + res2.first);
    }
  }


  for(int i = 0; i < N; i++) {
    seg1.update(L[i], R[i], -1);
    auto res1 = seg1.query(0, xs.size());
    if(res1.second < N - 1) res1.first = 0;
    chmax(ret, res1.first + xs[R[i]] - xs[L[i]]);
    seg1.update(L[i], R[i], 1);
  }
  cout << ret << endl;
}




Measured memory_bytes: 124904