#pragma GCC optimize("O2")
#include <algorithm>
#include <array>
#include <bit>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfenv>
#include <cfloat>
#include <chrono>
#include <cinttypes>
#include <climits>
#include <cmath>
#include <compare>
#include <complex>
#include <concepts>
#include <cstdarg>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <fstream>
#include <functional>
#include <initializer_list>
#include <iomanip>
#include <ios>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <new>
#include <numbers>
#include <numeric>
#include <ostream>
#include <queue>
#include <random>
#include <ranges>
#include <set>
#include <span>
#include <sstream>
#include <stack>
#include <streambuf>
#include <string>
#include <tuple>
#include <type_traits>
#include <variant>

//#define int ll
#define INT128_MAX (__int128)(((unsigned __int128) 1 << ((sizeof(__int128) * __CHAR_BIT__) - 1)) - 1)
#define INT128_MIN (-INT128_MAX - 1)

#define clock chrono::steady_clock::now().time_since_epoch().count()

#ifdef DEBUG
#define dbg(x) cout << (#x) << " = " << x << '\n'
#else
#define dbg(x)
#endif

namespace R = std::ranges;
namespace V = std::views;

using namespace std;

using ll = long long;
using ull = unsigned long long;
using ldb = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
//#define double ldb

template<class T>
ostream& operator<<(ostream& os, const pair<T, T> pr) {
  return os << pr.first << ' ' << pr.second;
}
template<class T, size_t N>
ostream& operator<<(ostream& os, const array<T, N> &arr) {
  for(const T &X : arr)
    os << X << ' ';
  return os;
}
template<class T>
ostream& operator<<(ostream& os, const vector<T> &vec) {
  for(const T &X : vec)
    os << X << ' ';
  return os;
}
template<class T>
ostream& operator<<(ostream& os, const set<T> &s) {
  for(const T &x : s)
    os << x << ' ';
  return os;
}


signed main() {
  ios::sync_with_stdio(false), cin.tie(NULL);

  int n; cin >> n;
  vector<array<int, 2>> lr(n);
  for(auto &[l, r] : lr)
    cin >> l >> r;

  auto check = [&](vector<array<int, 2>> seg) {
    ranges::sort(seg);
    priority_queue<int, vector<int>, greater<int>> pq;
    for(int i = 1, ptr = 0; i <= n; i++) {
      while(ptr < n and seg[ptr][0] == i)
        pq.push(seg[ptr++][1]);
      if (pq.empty() or pq.top() < i)
        return false;
      pq.pop();
    }
    return true;
  };

  int l = *ranges::partition_point(views::iota(-n, INT_MAX), [&](int x) { 
    vector<array<int, 2>> v(n);
    for(int i = 0; i < n; i++)
      v[i] = {max(1, lr[i][0] - x), n};
    return !check(v);
  });

  if (l == INT_MAX) {
    cout << 0 << '\n';
    return 0;
  }

  int r = *ranges::partition_point(views::iota(l, INT_MAX), [&](int x) {
    vector<array<int, 2>> v(n);
    for(int i = 0; i < n; i++)
      v[i] = {max(1, lr[i][0] - x), min(n, lr[i][1] - x)};
    return check(v);
  });

  cout << r - l << '\n';

  return 0;
}