typedef long long ll;
typedef long double ld;
#include <bits/stdc++.h>
using namespace std;
#define int long long

signed main(){
    ll n,m;
    std::cin >> n>>m;
    vector<pair<ll,ll>> p(m);
    for (int i = 0; i < m; i++) {
        ll a,b;
        std::cin >> a>>b;
        p[i] = {b,a};
    }
    sort(p.begin(),p.end());
    ll now = 0;
    ll ans = n*2-2;
    for (int i = 0; i < m; i++) {
        if(now<=p[i].second){
            now = p[i].first;
            ans--;
        }
    }
    std::cout << ans << std::endl;
}