#include <algorithm>
#include <iostream>
#include <queue>
using namespace std;
typedef long long ll;
typedef pair<int, int> P;

int main()
{
    int n;
    cin >> n;
    P p[200005];
    for (int i = 0; i < n; i++)
    {
        cin >> p[i].first >> p[i].second;
    }
    int l = 0;
    sort(p, p + n);
    for (int i = 0; i < n; i++)
    {
        l = max(l, p[i].first - (i + 1));
    }
    ll ok = l - 1, ng = 2000000000;
    while (abs(ok - ng) > 1)
    {
        ll k = (ok + ng) / 2;
        int j = 0;
        priority_queue<ll, vector<ll>, greater<ll>> que;
        bool f = true;
        for (int i = 1; i <= n; i++)
        {
            while (j < n && p[j].first <= i + k)
            {
                que.push(p[j++].second);
            }
            if (!que.size() || que.top() < i + k)
            {
                f = false;
                break;
            }
            que.pop();
        }
        if (f)
        {
            ok = k;
        }
        else
        {
            ng = k;
        }
    }
    cout << ok - l + 1 << endl;
}