#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
    int n, m;
    cin >> n >> m;

    vector<pair<int, int>> megallok(m);

    for(int i = 0; i < m; i++) {
        cin >> megallok[i].first >> megallok[i].second;
    }

    sort(megallok.begin(), megallok.end());
    int eredmeny = megallok[0].first - 1;

    int i = 0;
    while(i < megallok.size()) {
        if(megallok[i].second < megallok[i + 1].first) {
            eredmeny += megallok[i + 1].first - megallok[i].second;
            i++;
        } else if(megallok[i].second < megallok[i + 1].second) {
            i++;
        } else if(megallok[i].second >= megallok[i + 1].second) {
            megallok.erase(megallok.begin() + i + 1);
        }
    }
    eredmeny += n - megallok[megallok.size()].second;

    cout << eredmeny;

    return 0;
}