#include <bits/stdc++.h>
const long long N = 1000006;
using namespace std;
const long long MOD = 1000000007LL;
template <typename T>
T gcd(T a, T b) {
  if (a == 0) return b;
  return gcd(b % a, a);
}
template <typename T>
T power(T x, T y, long long m = MOD) {
  T ans = 1;
  while (y > 0) {
    if (y & 1LL) ans = (ans * x) % m;
    y >>= 1LL;
    x = (x * x) % m;
  }
  return ans % m;
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  if (n == 1) {
    cout << "0";
    return 0;
  }
  multiset<long long> l, r;
  vector<pair<long long, long long> > v;
  for (long long(i) = (0); i < (n); i++) {
    long long x, y;
    cin >> x >> y;
    l.insert(x);
    r.insert(y);
    v.emplace_back(make_pair(x, y));
  }
  long long ans = 0;
  for (long long(i) = (0); i < (n); i++) {
    l.erase(l.find(v[i].first));
    r.erase(r.find(v[i].second));
    long long dist = max(0LL, *r.begin() - *l.rbegin());
    ans = max(ans, dist);
    l.insert(v[i].first);
    r.insert(v[i].second);
  }
  cout << ans;
}
