#include <bits/stdc++.h>
using namespace std;
int scanst(char *a) {
  int i = 0;
  char c = 0;
  while (c < 33) c = getchar();
  while (c > 33) {
    a[i++] = c;
    c = getchar();
  }
  a[i] = 0;
  return i;
}
template <typename T>
bool scan(T &n) {
  n = 0;
  bool got = false;
  bool negative = false;
  char c = getchar();
  if (c == EOF) return false;
  while (c<'0' | c> '9') {
    if (c == '-') negative = true;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    got = true;
    n = n * 10 + c - 48;
    c = getchar();
  }
  if (negative) n = ~(n - 1);
  return got;
}
template <typename T>
inline T GCD(T a, T b) {
  a = abs(a);
  b = abs(b);
  while (b) {
    a = a % b;
    swap(a, b);
  }
  return a;
}
template <typename T>
inline T LCM(T x, T y) {
  T tp = GCD(x, y);
  if ((x / tp) * 1. * y > 9e18) return 9e18;
  return (x / tp) * y;
}
template <typename T>
inline T BigMod(T A, T B, T M) {
  T ret = 1;
  while (B) {
    if (B & 1) ret = (ret * A) % M;
    A = (A * A) % M;
    B = B >> 1;
  }
  return ret;
}
template <typename T>
inline T InvMod(T A, T M) {
  return BigMod(A, M - 2, M);
}
long long gcdr(long long a, long long b) {
  if (a == 0) return b;
  return gcdr(b % a, a);
}
long long max(long long a, long long b) {
  if (a > b) return a;
  return b;
}
long long min(long long a, long long b) {
  if (a < b) return a;
  return b;
}
void FastIO() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.precision(20);
}
int main() {
  FastIO();
  long long n, m, p, q, i, j;
  while (cin >> n) {
    vector<pair<long long, long long> > V;
    for (i = 0; i < n; i++) {
      long long x, y;
      cin >> x >> y;
      V.push_back(make_pair(x, y));
    }
    if (n == 1) {
      cout << abs(V[0].first - V[0].second) << endl;
      continue;
    } else if (n == 2) {
      cout << max(abs(V[0].first - V[0].second), abs(V[1].first - V[1].second))
           << endl;
      continue;
    }
    sort(V.begin(), V.end());
    pair<long long, long long> first;
    first = V[0];
    pair<long long, long long> second;
    second = V[0];
    long long indexf = 0, indexs = 0;
    for (i = 1; i < n; i++) {
      if (V[i].first > first.first) {
        first = V[i];
        indexf = i;
      } else if (V[i].first == first.first) {
        if (V[i].second < first.second) {
          first = V[i];
          indexf = i;
        }
      }
      if (V[i].second < second.second) {
        second = V[i];
        indexs = i;
      } else if (V[i].second == second.second) {
        if (V[i].first > second.first) {
          second = V[i];
          indexs = i;
        }
      }
    }
    long long l = 0, r = 1e12;
    for (i = 0; i < n; i++) {
      if (indexf == i) {
        continue;
      }
      l = max(l, V[i].first);
      r = min(r, V[i].second);
    }
    long long ans = 0;
    ans = max(ans, (r - l));
    l = 0;
    r = 1e12;
    for (i = 0; i < n; i++) {
      if (indexs == i) {
        continue;
      }
      l = max(l, V[i].first);
      r = min(r, V[i].second);
    }
    ans = max(ans, r - l);
    cout << ans << endl;
  }
}
