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

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());

    int ans = 0;
    for (int k = 0; k < lr.back().first; ++k) {
        bool ok = true;

        std::priority_queue<int, std::vector<int>, std::greater<int>> pq;

        for (int i = 1, j = 0; i <= n; ++i) {
            while (j < n and lr[j].first <= k + i) {
                pq.push(lr[j++].second);
            }
            if (pq.empty() or pq.top() < k + i) {
                ok = false;
                break;
            }
            pq.pop();
        }
        if (ok) {
            ++ans;
        }
    }
    std::cout << ans << std::endl;
}