#include <iostream>
#include <vector>
#include <algorithm>
 
using namespace std;
 
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
 
    int n;
    cin >> n;
 
    vector<pair<int, int>> vec;
    while (n--)
    {
        int l, r;
        cin >> l >> r;
        vec.push_back({l, r});
    }
 
    sort(vec.begin(), vec.end());
    int l = vec[0].first, r = vec[0].second;
    int result = 0;
    for (int i = 1; i < vec.size(); ++i)
    {
        if (vec[i].first <= r) // 有重疊
            r = max(r, vec[i].second);
        else
        {
            result += r - l;
            l = vec[i].first;
            r = vec[i].second;
        }
    }
    result += r - l;
    cout << result;
 
    return 0;
}
 

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