#include <algorithm>
#include <cassert>
#include <functional>
#include <iostream>
#include <optional>
#include <queue>
#include <vector>

bool solve(int n, const std::vector<std::pair<int, int>>& lr, int k) {
    assert(std::is_sorted(lr.begin(), lr.end()));
    std::priority_queue<int, std::vector<int>, std::greater<int>> pq;
    for (int v = k + 1, j = 0; v <= k + n; ++v) {
        while (j < n and lr[j].first <= v) pq.push(lr[j++].second);
        assert(pq.size());
        if (pq.top() < v) return false;
        pq.pop();
    }
    return true;
}

std::optional<int> get_min_k(int n, std::vector<std::pair<int, int>> lr) {
    assert(std::is_sorted(lr.begin(), lr.end()));
    int k = 0;
    for (int i = 1; i <= n; ++i) k = std::max(k, lr[i - 1].first - i);
    return solve(n, lr, k) ? std::make_optional(k) : std::nullopt;
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int n;
    std::cin >> n;

    std::vector<std::pair<int, int>> lr(n);
    for (auto& [l, r] : lr) std::cin >> l >> r;
    std::sort(lr.begin(), lr.end());

    auto min_k = get_min_k(n, lr);
    if (not min_k) {
        std::cout << 0 << std::endl;
    } else {
        int ok = *min_k, ng = 1000000000;
        while (ng - ok > 1) {
            int k = (ok + ng) / 2;
            (solve(n, lr, k) ? ok : ng) = k;
        }
        std::cout << ok - *min_k + 1 << std::endl;
    }
}