#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 j = 0;
    for(int i = 1; i < n; i++) {
        if(i >= megallok[j].second) {
            j++;
            i--;
            continue;
        }
        if(j >= megallok.size()) {
            eredmeny++;
        } else if(i < megallok[j].first) {
            eredmeny++;
        } else if(i == megallok[j].second - 1) {
            j++;
        }
    }

    cout << eredmeny;

    return 0;
}