#ifndef ONLINE_JUDGE
#define _GLIBCXX_DEBUG
#endif
#include <bits/stdc++.h>
using namespace std;

#define pass (void)0
#define INF (1<<30)-1
#define INFLL (1LL<<60)-1
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define rep2(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define repr2(i, a, b) for (int i = (int)(b) - 1; i >= (int)(a); i--)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) ((int)(x).size())
#define YesNo(cond) cout << ((cond) ? "Yes\n" : "No\n")
#define YESNO(cond) cout << ((cond) ? "YES\n" : "NO\n")

using ll = long long;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using vi = vector<int>;
using vl = vector<ll>;
using vvi = vector<vi>;
using vvl = vector<vl>;

template <typename T> void print(const T& value) { cout << value << "\n"; }
template <typename T> void print(const vector<T>& vec) { for (auto& v : vec) cout << v << " "; cout << "\n"; }
template <typename T> void input(vector<T>& vec) { for (auto& v : vec) cin >> v; };
template <typename T> bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; } return false; }
template <typename T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } return false; }

#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using vm = vector<mint>;

ll N;
vector<pll> LR;

ll func(ll k) {
    ll idx = 0;
    priority_queue<ll, vector<ll>, greater<ll>> que;
    rep2 (i, 1, N+1) {
        ll n = i+k;
        while (idx < N && LR[idx].first <= n) {
            que.push(LR[idx].second);
            idx ++;
        }
        if (que.empty()) return -1;
        if (que.top() < n) return 1;
        que.pop();
    }
    return 0;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(10);

    cin >> N;
    rep (i, N) {
        ll L, R;
        cin >> L >> R;
        LR.push_back({L, R});
    }

    sort(all(LR));

    ll left = -1;
    ll right = 1000000000LL;
    while (left+1 < right) {
        ll mid = (left+right)/2;
        if (func(mid) == -1) {
            left = mid;
        } else {
            right = mid;
        }
    }
    ll L = left+1;

    left = -1;
    right = 1000000000LL;
    while (left+1 < right) {
        ll mid = (left+right)/2;
        if (func(mid) == 1) {
            right = mid;
        } else {
            left = mid;
        }
    }
    ll R = right-1;

    print(R-L+1);
}