#include <bits/stdc++.h>
using namespace std;
const long long MOD1 = 1000000007;
const long long MOD2 = 998244353;
typedef long long ll;
typedef pair<ll, ll> P;
const long long INF = 1e17;
void solve() {
    ll N, M; cin >> N >> M;
    vector<P>A(M);
    for (ll i = 0; i < M; i++) {
        cin >> A[i].second >> A[i].first;
    }
    sort(A.begin(), A.end());
    ll ans = 0, pos = 0;
    for (ll i = 0; i < M; i++) {
        if (A[i].second >= pos) {
            ans++;
            pos = A[i].first;
        }
    }
    cout << 2 * (N - 1) - ans << endl;
}
int main() {
    ll T = 1; //cin >> T;
    while (T--) {
        solve();
    }
}