#include <bits/stdc++.h>
using namespace std;
bool isUpper(char c) { return (c >= 'A' && c <= 'Z'); }
bool isLower(char c) { return (c >= 'a' && c <= 'z'); }
bool iplpha(char c) { return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z'); }
bool isnum(char c) { return (c >= '0' and c <= '9'); }
bool isalnum(char c) {
  return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') ||
         (c >= '0' && c <= '9');
}
char toUpper(char c) { return isUpper(c) ? c : c - 'a' + 'A'; }
char toLower(char c) { return isLower(c) ? c : c + 'a' - 'A'; }
bool isvowel(char c) {
  c = toLower(c);
  return (c == 'a' or c == 'e' or c == 'i' or c == 'i' or c == 'o' or
          c == 'u' || c == 'y');
}
template <typename t>
t gcd(t a, t b) {
  a = abs(a), b = abs(b);
  return ((b == 0) ? a : gcd(b, a % b));
}
template <typename t>
t lcm(t a, t b) {
  return (a * (b / gcd(a, b)));
}
template <typename T>
T modpow(T base, T exp, T modulus) {
  base %= modulus;
  T result = 1;
  while (exp > 0) {
    if (exp & 1) result = (result * base) % modulus;
    base = (base * base) % modulus;
    exp >>= 1;
  }
  return result;
}
string toLowerCase(string s) {
  for (int i = 0; i < s.size(); i++) {
    if (!isLower(s[i])) {
      s[i] = toLower(s[i]);
    }
  }
  return s;
}
string toUpperCase(string s) {
  for (int i = 0; i < s.size(); i++) {
    s[i] = toUpper(s[i]);
  }
  return s;
}
template <typename T>
void cumulative(T *a, T *b, T n) {
  for (int i = 0; i < n; i++) {
    i ? b[i] = b[i - 1] + a[i] : b[i] = a[i];
  }
}
bool ispal(string s) {
  long long lo, hi;
  lo = 0;
  hi = s.length() - 1;
  while (lo <= hi) {
    if (s[lo] != s[hi]) {
      return 0;
    }
    lo++;
    --hi;
  }
  return 1;
}
template <class T>
string toString(T n) {
  string v = "";
  while (n) {
    v.push_back(n % 10 + '0');
    n /= 10;
  }
  reverse(v.begin(), v.end());
  return v;
}
long long binary_search(vector<long long> a, long long n, long long key) {
  long long lo = 0;
  long long hi = n - 1;
  while (lo <= hi) {
    long long mid = (lo + hi) / 2;
    if (a[mid] == key) {
      return mid;
    } else if (a[mid] < key) {
      lo = mid + 1;
    } else {
      hi = mid - 1;
    }
  }
  return -1;
}
int main() {
  long long n;
  cin >> n;
  vector<pair<long long, long long> > v;
  for (int i = 0; i < n; i++) {
    long long x, y;
    cin >> x >> y;
    v.push_back(make_pair(x, y));
  }
  sort(v.begin(), v.end());
  vector<pair<long long, long long> > pre(n + 2, make_pair(0, 1000000007)),
      suff(n + 2, make_pair(0, 1000000007));
  for (int i = 0; i < n; i++) {
    pre[i + 1].first = max(pre[i].first, v[i].first);
    pre[i + 1].second = min(pre[i].second, v[i].second);
  }
  for (int i = n - 1; i >= 0; i--) {
    suff[i + 1].first = max(suff[i + 2].first, v[i].first);
    suff[i + 1].second = min(suff[i + 2].second, v[i].second);
  }
  long long ans = 0;
  for (int i = 0; i < n; i++) {
    ans = max(ans, min(pre[i].second, suff[i + 2].second) -
                       max(pre[i].first, suff[i + 2].first));
  }
  cout << ans << endl;
}
