#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1e9 + 7;
const long double PI = 4 * atan((long double)1);
const long long INF = 1e18;
const long long NINF = -1e18;
long long get_hash(string s) {
  long long N = 1000001;
  long long base[N], A = 11, MD = 1110111110111;
  base[0] = 1;
  for (long long i = (1); i < (N); ++i) base[i] = (base[i - 1] * A) % MD;
  long long hs = 0;
  for (long long i = (0); i < (s.size()); ++i) {
    hs += (s[i] * base[i]);
    hs %= MD;
  }
  return hs;
}
long long power(long long a, long long n) {
  long long res = 1;
  while (n) {
    if (n % 2) res *= a;
    a *= a;
    n /= 2;
  }
  return res;
}
vector<string> vec_splitter(string s) {
  s += ',';
  vector<string> res;
  while (!s.empty()) {
    res.push_back(s.substr(0, s.find(',')));
    s = s.substr(s.find(',') + 1);
  }
  return res;
}
void debug_out(vector<string> __attribute__((unused)) args,
               __attribute__((unused)) long long idx,
               __attribute__((unused)) long long LINE_NUM) {
  cerr << endl;
}
template <typename Head, typename... Tail>
void debug_out(vector<string> args, long long idx, long long LINE_NUM, Head H,
               Tail... T) {
  if (idx > 0)
    cerr << ", ";
  else
    cerr << "Line(" << LINE_NUM << ") ";
  stringstream ss;
  ss << H;
  cerr << args[idx] << " = " << ss.str();
  debug_out(args, idx + 1, LINE_NUM, T...);
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long n;
  cin >> n;
  vector<pair<long long, long long> > v;
  for (long long i = (0); i < (n); ++i) {
    long long l, r;
    cin >> l >> r;
    v.push_back({l, r});
  }
  sort(v.begin(), v.end());
  pair<long long, long long> pref[n + 1], suff[n + 1];
  pref[0] = {0, INF};
  suff[n] = {0, INF};
  for (long long i = (0); i < (n); ++i) {
    long long x = v[i].first;
    long long y = min(pref[i].second, v[i].second);
    pref[i + 1] = {x, y};
  }
  for (long long i = (n)-1; i >= (0); --i) {
    long long x = v[n - 1].first;
    long long y = min(suff[i + 1].second, v[i].second);
    suff[i] = {x, y};
  }
  long long maxa = 0;
  for (long long i = (0); i < (n); ++i) {
    long long x = max(pref[i].first, suff[i + 1].first);
    long long y = min(pref[i].second, suff[i + 1].second);
    if (y - x > maxa) maxa = y - x;
  }
  cout << maxa;
  return 0;
}
