#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;
using ll = long long;

template<typename T>
bool ord(T &x, T & y){
    return x.second < y.second;
}


int main(){

    int N, M, now=0, ans=0;
    cin >> N >> M;
    vector<pair<int, int>> AB(M);
    for (int i=0; i<M; i++) cin >> AB[i].first >> AB[i].second;

    sort(AB.begin(), AB.end(), ord<pair<int, int>>);
    
    for (int i=0; i<M; i++){
        if (now <= AB[i].first){
            ans++;
            now = AB[i].second;
        }
    }

    cout << (N-1)*2-ans << endl;

    return 0;
}