#include <bits/stdc++.h>
using namespace std;

int n, m, d, t;
pair<int, int> a[100000];

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

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

    sort(a, a + m);

    d = (n - 1) * 2;

    for (int i = 0; i < m; i++) {
        if (t <= a[i].second) {
            d--;
            t = a[i].first;
        }
    }

    cout << d << endl;
}